I had this exact same problem in my cobra replica's 302. It would stumble when I got on it, on the street, but run smooth in the garage. we replaced the coil. we rebuilt the distributor. Nada. we fiddle-farted around for hours trying to solve the problem, and finally we were SURE it was the distributor - we took a distributor out of another 302 and all of a sudden the car ran great. Aha! I popped for a new stock distributor, put it in and lo and behold, the car ran like garbage again.

As it turns out, the one thing we DIDN'T change was the rotor - it looked fine, why change it. We put the rotor from the other car into the cobra and it ran great. I ran to Kragen, spent $6 for a new rotor, and the car ran like a top.

Moral: Try the simple stuff first.

All the best,
Tag