does an RB have to be bushed for a Mech Roller Lifter

Nope, but they are Damn pricey! Can't understand why there is such a price difference between the "Other" brands and Mopars. Doesn't take any additional work to produce these things.. Pisses me off! I guess I am cheap but Damn!!

Your choice as far as Hyd. vs Mech..

I have used Comps with no issues.