I am running the Comp Cams Ultra Pro Magnums.  They have been running strong since 2014 - in a couple of different engine builds OBTW.

I liked the idea of the steel bodies vs. the aluminum that you get with many of the other offerings (Scorpion, Harland Sharp, etc.)

I also liked the big fulcrum bearing.

It's pretty hard for me to compare these vs. all the others (and say they are better), but my engine builder  - who generally casts dispersions on all engine parts that he has not had direct (and good) experiences with - did not complain about this choice of mine.

My heads were machined for the 7/16" pedestal.

https://www.jegs.com/i/COMP-Cams/249/1630-16/10002/-1

I looked at the Yella Terras, but the difficulty in getting a set, and the cost were factors in my decision.

Rocky

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The main advantage of roller rockers is a drop in engine friction and resulting lower oil temps. They do NOT give measurably more power or torque unless you change the stock 1.73:1 rocker ratio and/or other parts. Adjustability is important when you add roller rockers since that change requires specific length hardened pushrods for correct geometry. Stock steel sled rocker arms are very forgiving with geometry but rollers are not. The stock pushrods do not rub anything so are not hardened, while with an adjustable valvetrain there are hardened guide plates that contact hardened pushrods. These are all stock Boss 351 parts.

Not familiar with Scorpion's bolt-down system. There are (or were) kits that allowed one to add roller rockers without guide plates, by using special pedestal-plates that held a plastic guide bushing (part of the kit) for each pushrod. If you can find a NOS kit or will be satisfied with Scorpion, the Advantages: cheap; no need to risk cutting cast iron rocker pedestals to Boss dimensions and doing it wrong (which happens & can waste stock cylinder heads. HRM had a recent story on a poorly pro-machined stock 351-C engine that took some $4000(?) to fully diagnose and correct).

Disadvantages-  I think it's more difficult to arrive at the correct length pushrods needed with any roller rockerarm due to a stock geometry engine's lack of adjustability with bolt-down rockers. Previous head work also changes that geometry; the guide bushings in a kit wear and need replacing over time; the whole system is not as strong as Ford or ARP rocker studs & the other Boss-351 parts, so such an engine will be rpm-limited to more-or-less stock redline.

Other choices: ALL aftermarket aluminum heads are already cut for a fully adjustable valvetrain, they are each about 40 lbs lighter than cast iron, and all have the more efficient Boss-351 style closed combustion chamber design. All accept stock or aftermarket Boss parts. Pro engine shops say that if you're looking for more power, by the time you suitably modify stock iron heads, you will be into the engine for about what an assembled set of aluminum heads cost.

I personally would never use PAC or any other beehive spring on an engine. After I had a coil break, you only have one for each valve, the damage is terrible. Take a look at conical valve springs if you want to save weight and not use exotics.

Thank you for the  comment!  Always valuable input here.

Rocky I will definitely look at those rockers. That's what I want is improved function, with reliability. I think I breezed past those for some reason in the past. They look like a great option...especially since you've been running them since 2014! I want to have the confidence of jumping in the car, driving for 500 miles and not get stuck somewhere.

Mr. Bosswrench! I can always count on your great info! I never thought about a machinist screwing up a head when machining the pedestals to accept a 7/16 stud!  Fortunately, I do have three sets of 4V heads but one is an open chamber set. But I should have a backup if needed. Also the machinist I found only 5 miles from me had races the 351C for many many years, so hopefully that experience will add to his machining capabilities.  And do vaguely remember the there was a setup that didn't require pushrod guides. I'll look at that also.

Bdud, never thought about a beehive breaking....will definitely look at the conical springs or just go with a more conventional spring that has a damper which if the main spring broke might still save the valve from major damage. Thank you, great advice!

You're correct- beehive springs have amassed a record of occasional breakage both in competition and on the street, and since they are always run as single springs, spring breakage is almost always instantly followed by that now loose valve following the piston down into the cylinder. Massive damage usually follows as the piston travels up with the valve now inside the cylinder, including split cylinder walls and destroyed heads. Aluminum heads and blocks can be repaired easily but not cheaply.  Serialized iron blocks with a damaged cylinder can be sleeved but a punctured iron head is a total loss.

FWIW: conical springs such as those sold by Comp Cams have the same small tops and lightweight retainers like beehives do, but are straight-wall-shaped such that a second conical inner spring can be fitted for 'insurance'. Beehive springs have a curved profile; so far, no one has made an internal 'insurance' spring to fit. Unlike straight dual springs with dampers, the inner and outer springs of  conicals do not contact each other or use a damper so friction and oil heating   stays low.

The performance parameters seem to be identical for beehive and conical springs (light weight, small retainers, low oil heating and rev-range extension). When I upgrade my own engine, I will likely use dual conical springs but NOT Ti retainers; tool steel retainers are stronger, do not abrade like Ti and are within grams in weight.