I also run a Bear 13" kit on the front purchased ~10 years ago. I first installed it with the iron master supplied by Bear and a reman OE 9" single diaphragm booster. The Bear hoses did not work as supplied for rear mount calipers - too short. I wound up using them as a pattern by cutting them in half and using a piece of poly tube slipped over the flex part to join the halves. That way I could adjust length and orientation of the ends. With T bars out, I tried full jounce, full rebound and full left and right adjusting the hose length and orientation until it worked. I used some hose clamps to lock the poly tube in position and sent the mock-ups off to Inline Tube. A week or so later they sent back a set of perfect hoses.

Maybe/hopefully Baer or Dr Diff have the hoses figured out now.

With that I had good functional front brakes... but not enough line pressure for max effort stopping. As I got more serious about track use, that needed fixed. First was the 8" dual booster. I got it from Mancini, however Dr Diff sells them also. Straight forward installation... at least no harder than a stock booster. Working on the linkage under the dash is not my favorite but as the saying goes, just nuts and bolts. The back of the dual booster is a bit larger diameter so the hole in your original firewall re-enforcing plate will be a little small... either hog it out or get the new plate that fits (which I did). The dual booster was better but still not 100%. More pressure needed. I added a Dr Diff 15/16" master and it is good now. With sticky 200 TW handling tires, I have all the brakes I can use.

That took care of the front. My rear drums I burned up at a track day and switched to the Dr Diff Cobra based rear kit (mock up pics attached). As advised by Dr Diff, one axle shaft needed slightly lengthened to get contact with the thrust button and provide effective adjustment for the tapered bearings. I welded a hardened washer on the end of the shaft and machined it down based on test fit to get it dialed in.

The system works great with EBC yellow pads. Front and rear are balanced and great stopping capability on a road course with repeated laps.

PS: You asked about vacuum.... I have ~13" at idle after tuning. Before tuning it was under 10". Works fine for around town driving. Also, mine is manual transmission so while braking in gear, probably 20+" vacuum. If yours is lower, probably need a vacuum pump or hydroboost.