Mancini sells a really nice roller button. Diamond Racing Products is the brand. Cost about $30. In most engines it will fit without any mods. I have had to press an indention in a cover once or twice as it was too tight.
it is the rotation of the dist./oil pump shaft that causes the cam to try to go out the back of the block on BB mopars and sb chevys, that is why no thrust plate or button. On a sb mopar the placement of the dist./oil pump trys to make the cam go out the front of the engine, therefore a thrust plate is used. I don't know if it necessary to put a button on a BB with a flat tappet but it won't hurt to have it, however it can be a hassle sometimes. I do put them in solid lifter flat tappet cammed BB mopars that I build.