If you haven’t figured this out yet then I’d say you can try unbolting the master cylinder and bending it and the lines forward to see if that will give you enough room.
Gently of course.

If you do end up completely removing the master cylinder then do all your brake bleeding with the key off and/or the ABS fuse removed.
And if you can, do a reverse bleed by pumping fluid into the calipers, thus pushing air out into the master cylinder reservoir.

Why do you want to replace the brake booster?

It's failing the vacuum hold test, and I'm noticing more pedal effort being required to bring the KJ down to a stop. Brake fluid levels are constant, so suspect a failing booster rather than hydraulics. Pads & discs are new enough (18 months) that I'm not concerned about them, and appear to have worn evenly in both cases with good meat still remaining on the pads.

When I replaced my calipers and rubber brake lines, I used the a pressure bleeder by Motive Products.
It worked like a champ, no issues with anti-lock controller.
There are some other power bleeder brands available that I am sure will work equally well.
Bleed them with engine OFF, and key OFF.

Classic signs of a failed diaphragm. What often happens is you get oil fumes in the booster & they destroy the diaphragm. This can happen on cool down when there is a leaky non return valve in the vacuum line.

Yep, been through this many times before and the symptoms fit. I did try swapping out just the check valve on the booster, and while that helped a bit, the problem continues. There are also three or four check valves in the vacuum path between the booster and the turbo vane gubbins (I'm including the one behind the glovebox for the A/C in that count) that are planned for replacement just to give my OCD some satisfaction.