I *think* the advance mechanism, weights, springs are interechangabel with the electronic distributors. Exception will be the later Mopar Performance version made by Mallory. (see some pictures on my website).

Well if you're OK with a ECU box, you could go back to the electronic distributor. You can use a parts store ECU for more reliability - or at least keep it as back up for one of the Street MP ECUs.
You're engine is such that a multi-spark, capacitive discharge ignition may be worth the expense. If you go with an MSD 6A, 6T, or 6C any of the distribuors you already have will work. You'll need a matching coil. Of course you'll still need to get the advance curve, so it only solves your current problem if you buy one of the more easily adjustable distributors.

edit: Its a time-money equation only you can answer. My inclination is to figure this out and get running.