These are not OEM roller lifter cams and lifters. They are aftermarket.
You can't rely on a near 100% dependability. All you can do is simplify the valve train and/or keep changing out the breaking components.
Rene, you don't need to change out the valve springs. New push rods with stock flat lifter cams should be stock, not custom.
You are going to change out the lifters and cam anyway. This isn't as complicated as you think if you go to a flat lifter cam.
If you switch, you can get a cam kit. Cam, lifters and matching springs.
So I don't understand the issue some have with adding ZDDP to the oil? You are just returning that oil mix to the original formula that the car was designed with.
The issue now with ZDDP is that it has the tendency to foul catalitic converters. There are none on Panteras to foul.
US law requires OEM manufacturers to warranty the emission systems for 100,000 miles. Cats are expensive to replace.
Current OEM manufacturers went to roller lifter cams for that reason and because they are aiming at a Fleet fuel consumption average and the roller lifters help that Fleet number. There is no other reason.
A roller lifter camshaft can be ground with a steeper lobe ramp then a flat lifter cam can. So that permits a more radical cam timing with better everyday manners BUT the cams you are selecting are too mild to take advantage of that, so then what is the advantage of a roller lifter cam?
Simplify. It is the best course of action.
Incidentally, what does the lifter bore in the block look like? Aren't you risking damaging those in the block with another lifter failure?