I replaced the points on my GM distributor ('74 Pontiac 350)
with Pertronics electronics, an MSD box, and an Accell adjustable vacuum advance.  Big improvement, works great... My problem:  I took the distributor apart recently and discovered that there is no positive stop to keep the advance plate inside the distributor from advancing way past my desired maximum total advance of 34 degrees (crankshaft degrees).
Is something missing from when I removed the original points? Shouldn't there be a stop somewhere?  Is there an accepted way to lock such a distributor in so as not to exceed max advance? (I start off with 13 degrees at idle.)  

I installed several of these on my buddies cars and never heard of this. This was the last year for the points dist. because the HEI showed everywhere in 75. The points and condenser come off the plate and don't have anything else attached to them. The only thing I can think of is that the mechanical advance springs or weights are missing off the dist. They are under the rotor. Without the springs the mechanical advance will go instantly to around 50 degrees advanced. Also check to see if the vacuum advance is correctly attached. It has a slot that a rod comes up from the bottom that limits the advance.