just finished a rebuild on my 3l and and having a few issues..im just a backyrd mechanic so i dont know where i went wrong.i had three dead motors sitting in my shop so i thought i would build 1 good one out of the three.when removing the pistons on the block i was using a few pistons broke so i used pistons from a different block..is this ok?after putting it back together it would not start.thought it was a timing issue so i played with that for a while but it did not get me anywhere.when i try to startit it cranks over good but then slows right down after a few cranks like the battery is dead but its fully charged..what have i gotten myself into..any help appreciated