My starter jumps right away when i try to fire up my small block 400 snd grinds a bit. Usually if i try to crank over again, it gets stuck or something and doesn't do anything. Could it be the fact that i'm using the starter off my old 350? or are they all the same for small blocks? Please help and thanks in advanced...

Small Block Chevys used two different starters depending on which flywheel/flexplate they had. They are different for the 168 tooth flywheel/flexplate and the 153 tooth one.

Old GM starters often need a good rebuild. You can easily do that yourself with the cheap $10 rebuild kit available at your local auto parts stores. They replace the bendix, brushes, bushings, and other small parts like thrust washers. Most starters will be good as new again with this kit.