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.