A roller motor just means it has roller lifters instead of a flat tappets. Basically there’s a wheel that rides along the came instead of just a flat metal surface.
But anyway, 20/50? WTF? Now you are looking at starving the top of the engine at cold starts, especially when it’s cold out, and hurting yer gas mileage. If you need to use that heavy of an oil to keep oil pressure up, you’ve got some problems bud.
You said the truck is a factory 5.0. If you have the means to find a low mileage 302 long block, just swap it in. Then you don’t have to worry about new PCM’s/wiring etc. Quick and dirty. Then MAINTAIN the engine. Don’t skip oil changes. My ’91 has 150k miles on it’s 302, and it only does work (towing, hauling etc, it’s not a daily driver) and runs good, so I know they will last, as yours already has.