can someone id this crank number?

i had the motor upgraded 2 years ago. i had a falling out with the "builder", and never got any specs on this motor. i recently broke a valvespring, so i was able to dig in, and i was wondering if someone could id these numbers stamped on the front of the crank:

J 1 0 4 5 6 4 1

if so, thanks in advance...

jb