98 Chevy engine swap

Hello, my motor locked up so I found a beater truck that
had a good engine in it. My truck is a 98 Chevy k1500 and
the Truck was a 97 k1500. So it’s a 5.0 to5.7 engine swap.
Got the motor in and it will not run. It’s firing and we’re
getting fuel. All it does is turns over. We did remove the
distributor to have better access to the top bolts and did
turn the motor to get TDC. Not sure if the timing is off it
would seem like if it was off the would at least try to run
but it just turns over. We did get one backfire and that was
it. Swapped computers and still nothing.