Sounds like you got a couple of plug wires reversed.
Easy enough to do.

You've already done better than me when installing a chevy distributor. I don't think I've ever got one in the right way the 1st time. Always 180 degrees out. I crank, it backfires, then I take the distributor out and turn it around, then it works. Except for the time where I thought to myself "I always get this backwards. I'll just flip it around before trying to start it". Yep. You guessed it. That time I had it in right the 1st time.

regards,
Leon