Whats needed to fit roller cam into my 1971 340?

IIRC, even the Hughes hydraulic rollers sometimes don't have the band low enough for some of the 340 lifter bore chamfers. There are several threads here in the last 2 years on that topci so taking some time to look then up would be worthwhile. So the sure solution has been to go to solid rollers... but that is assuming you can find the right cam for your use in that line. There are fewer solids of any type set up for the lower RPM ranges, (if that dictated by the desired use).

BTW, I don't necessarily agree on the idea that rollers are just for all out effort. One of the key reasons is so that the lift to duration ratio can be made even higher than the most aggressive flat tappet cam ramps. It can be used give benefits all over: low, mid and high range torque.

FWIW: Knarly sound = poor mileage and, more often than not, less low end torque. They use a lot of overlap to get the sound, which costs in other areas. That may or may not be important to the OP.