yeah buddy, nothing sucks more than being a buget racer and blowing your goods to smitherings, been there done that.
Though I cant offer up too much insite as to what may have caused your problem, but my first guess would be a bearing/oil related issue of some sort causing the rod(s) to weld them selves to the crank then exit the stage left, been there done that too, it sucks, I feel your pain.
This may be a touigh pill to swallow but learn from it and you'll be better off in the long run.
Heres a suggestion for your next build:
If you dont already have one, plumb in a low oil pressure warning light, a BIG BRIGHT RED one.
Have it right in your face, the instant you see it come on, kill the power, it just might save you a few thousand dollars and or the entire motor, its easy to do and is a relatively inexepnsive detection system.
I teed into my oil pressure gauge fitting with a single wire idiot light sensor I bought from a local parts house, I paid all of $5 dollars for it, the light I used was old shift light I had laying around the shop, mounted it right next to my tach in clear view.
A oil accumlator is another good investment, though more expensive.
Hope you get back to racing soon.
Regards, Cp