225 six wont start

I recently had my mechanic put an old 225 slant six in my 66 cuda. My old motor threw a rod so i found a new block and bolted on the existing head that i had. The motor will crank and turn over but seems to not get any gas or fire. I have been told that even with a bad head the motor should at least start up a little. My mechanic has given up on it so i am wondering if any of you experts know of anything it could be Thanks