I tried the vacuum conversion also, but went back to the PM.
I bought a complete unit from the junkyard off an '86 Regal - $50.
I don't trust junkyard parts, so I bought a lifetime warranty master cylinder - $40.
The Casper vacuum block for the TTA wasn't available yet - I bought one of the two GM had - $85.
I installed the assembly & the vacuum booster unit from the junkyard leaked vacuum - lifetime warranty one - $90.
A couple times on the street when pulling out into heavy traffic (read WOT- maximum boost & no vacuum to operate the vacuum brake boost unit), I would have somebrain dead about 2-300' up the road also pull out. By the time I would realize the road is totally blocked (by the brain dead in the Toyota or the suv), i'd be over 40 mph & have to use both feet on the brake pedal to stop (also the traffic behind me is moving 40 - 50 mph.
I bought a vacuum booster pump for the early '80s Citation to give me vacuum to the brake booster all the time - $240.
After about a year the vacuum brake booster developed a vacuum leak. The leak was not steady & varied with every application & release of the brakes. Troubleshooting my IAC was a real hair puller until I figured out the vacuum brake unit was leaking. No problem, lifetime warranty, I got & installed another unit.
The now third vacuum brake booster developed a leak in abou a week. My last trip home from work with this vacuum booster unit was a nightmare. The computer was adding fuel to the leak & the TR was ideling at approximately 2k rpm or 70+ mph. At the seemed like thousands of RED lights, using both feet to hold the brakes, the TR would not idle & would die unless I fed it more footfeed - however it took both feet to hold the brakes. I guess I was fortunate the seat didn't break loose from the floor.
I got my money back for the vacuum booster & have a Citatation unused vacuum boost pump for sale & bought a lifetime warranty PM. My IAC is now adjusted properly & the PM always works (so far). The only problem with the PM install was that the old unit had blown the fuse.
You can do what you want & I have two friends local who have had no complaints about their vacuum conversions. I just couldn't see the difference in price - PM lifetime warranty - $199. Vacuum conversion - $505 & couldn't set IAC.
HTH,
Roger