Coming back with a build! Need advice!

It ran for 20 minutes, sounded great, back fired, and stalled out, tried restarting, and locked up.. will turn but only about 200* in either direction - have it torn down a little and see no signs of anything broken yet... no metal.. cam looks great.. everything is pointing to a exhaust valve kiss the piston, or a rod let go very gently, as there is no outside evidence to support it..

I was planning to drive the car home, but had to trailer it and just got really down for about a month as I just spent $3,500 on it.. (motor alone)