If I go with flat tappet (I won't though)what would I do about the lifters? My block is for roller lifters. I thought they were different from the la blocks?
Like 70aarcuda and myself as well with the MP create short block. Roller block, Hyd. lifters (W/a 292/.509 Hyd. purple cam.)
The difference between Magnum and "LA" blocks are lack of oil passages to feed the rockers for the "LA" engines and where the motor mounts are. Late model "LA" roller engines and some (If not all) Magnum engines have dual provisions for motor mounts.
Everything else swaps over. You'll be fine.
Back to the cam question for the moment. What cam are you looking at/thinking about?