It is very simple to see if your booster is working, drive it and stop. Then disconnect and plug the vacuum line to it, drive it and stop. You don't need an experienced mechanic to do that. As for brake systems.
Dual verses single is kind of an arguing point. The idea of dual is to make it safer. The idea is if you lose half your brakes you can still stop, however that only works if you lose the rears. The fronts however do 95% of your stopping so if you lose the fronts,(50/50 chance), you're not stopping. In all my cars I do switch to duals but I'm a mechanic and it's easy for me to design and switch the system. I bought my '65 Econoline a year ago and drive it daily with manual single drum brakes and have no stopping issues, I just painted it last week and will do a few upgrades now including dual power brakes. But I love to tinker.
As for
drum to disc, The only negatives to drums are' #1 if you are going to race it, they don't like repetitive braking. they get hot and glaze over the shoes and you lose brake power. #2 back in the day when the roads sucked wading threw deep puddles will lubricate the shoes and they wont stop until you drag the pedal for a while to dry them out. My '65 Falcon, '65 Econoline, and '76 CJ are all Drums and have never had this happen on any of them over the last 10 years.. #3 you have to maintain the brake adjustment on drums where discs adjust themselves. If you know how to use your self adjusters the drums will adjust themselves very well. I always check mine when I have it up in the air doing their oil changes.
I'm '70 years old , have literally had over 100 cars from the '50's to the '70's and have NEVER done a disc conversion to any of them, Have converted most of them to dual master, and did a few power conversions mostly because they were easy to do and you don't have to push as hard on the pedal.
Just my .70 cents. inflation, you know?
