just rebuilt runs bad

It's really awesome how everyone steps up to help out here. I hope to have the experience and knowledge to help others some day.

Here's the latest. With the MSD box sitting unattached on top of the fender and grounded to the battery, and MSD coil and distributor wires isolated from other wires to the extent possible, I started the motor. This time advancing the initial timing (turning dist. CC) from TDC a little more than I had in the past. I started the motor and NO Backfiring or metallic noises. The timing was between 15 and 17 BTDC, in the past it was anywhere between 0 and 12 BTDC. There is some hesitation when I gun the throttle but no metallic noises or backfire. I'm hoping hesitation can be corrected with some tweaking. It was late at night and I haven't had a chance to get back to it since. So I feel like i'm getting very close. Going to put the MSD stuff back where it was and see if the backfire and noise returns, also move the timing back to 10 BTDC or below.

To answer some of the new questions:
- The vacuum port in back of the carb is plugged
- I checked for vacuum leaks around the intake and carb by spraying carb cleaner
- Builder used PBM timing chain and gear set
- Didn't keep track of the plugs well enough to know which cylinders had the wetter plugs.
- Cylinder balance test and vacuum timing may be in the future if problems continue.

I'll have some time to work on the car tomorrow and will post an update.

Thanks for all the support and suggestions.