Art you asked about making a mechanical advance system work with boost. I have a solution, not sure it is optimal but I think it can work.
You set the initial, mechanical and vacuum advance to match the needs of the engine N/A (off boost). The vacuum of course will retract (retard) as soon as you lose vacuum and definitely once the boos starts. The mechanical will still do its thing ramping up with the centrifugal force as the motor rpms up. That'* when you program in the electonic boost retard to pull back the timing to counteract the mechanical advance and bring the total all back to 26ish degrees.
The vacuum is out of it so lets just talk about the mechanical and the boost retard. Lets say you are running an initial of 12 degrees. Then lets say you use the mechanical to bring it up to 32 degrees so the engine runs its best N/A. If you have the initial and mechanical all in by 2600 rpm you are going to want it back to about 22 on boost. Use the boost retard to pull back the timing to compensate. If you are running a total of 10 psi then while the motor mechanically is hitting 32 by 2600 rpm, the boost can be set for 1 degree for each pound a that will electronically pull it back to 22 at 10 psi. A good boost retard should allow incremental settings, such as 1.5 or 2.5 degrees per pound so you can pull it back exactly how much you want depending on how much boost you run. Let me know if you think that can work. You must make sure the electronics are working or you'll be sending your heads to the Moon, LOL. If it stops working.
I've been staying out of the garage because of 110 degree temps. But I've been doing my homework on making a front drive distributor. I took into consideration the thought you guys had about the shaft running in the sintered bearings on its side. SOOO!! I purchased a new Pro-Comp electronic billet distributor with the top roller bearing. I've blown apart the distributor already but I took a pic of the principle parts.
In it you can see the distributor, distributor shaft, the pump extension and the extension roller bearing and the hex drive shaft in the bearing.
This is the extension again. The top end of the pump extension pic shows the shoulder that is machined into the inside of the extension to seat the bearing.
The bearing normally installs into the top of the extension so it sits almost flush with the opening. Then the hex drive goes through the bearing and the pump would sit down into the slight relief (pocket) at the flange and the pump shaft would fit into the hex drive end. What I'm going to do is bring the bearing in from the opposite end of the extension and locate it about half way down the inside of the extension. Cut off the distributor housing shaft and have it machined down in steps so it fits in snug to the top of the extension. The first cut from the top of the distributor will match the first opening diameter of the extension, the second cut will match the reduced "step'" that originally stopped the bearing (the bearing shoulder). The following pics kind of lays out where everything will line up.
I think I found a machinist to work with. So I'll be taking it there soon.
With this set up the top of the distributor shaft will be riding in a roller bearing, the mid point of the shaft, where it will get machined to fit the hex shaft adaptor, will ride in a roller bearing, and the end be inserted into the pump drive hex receiver mounted on the cam. The last thing will be to cut the distributor shaft to length and have the end cut to a hex to fit the hex drive adaptor end.
The distributor I bought is a Chevy with a slip collar to locate it where I need it to be so that will allow some latitude in how long I make the housing shaft. I think it will work out fine. More pics coming as I get the machining done.