Finally got over to the shop and spent the afternoon pulling the carbs and intake manifolds off the 3.0 engine that is in the car. I confirmed that it is the matching numbers engine for the car, so I'll probably keep it, freshen it up and store it for a future buyer who may want to go back to original.
After removing the existing downdraft intake assembly (what a PITA!! Nearly EVERY nut and bolt is hard to reach!), I test fit my 3D printed manifolds. They fit OK, but I was chagrined to find that while the block of the M30 engine is tilted 30 degrees from vertical, they make up for some of this tilt in the head, so the intake flanges on the head are about 25 degrees. This is, apparently, why the commonly available manifolds (Karsundpartz, available from Pierce, Ireland, and others) are about 18 degrees. With my test manifolds the carbs are basically level, and very close to interfering with all sorts of things. The Karsundpartz units are shorter, and end up with the carbs tilted about 7 degrees from horizontal, which is pretty close to the 5 degrees recommended by Weber.
So, I think in the interest of time and money, I'll just go with the Karsundpartz units. I already ordered and received the Tii booster, and the thermostat offset spacer, so this looks pretty straightforward. The 3D trumpets seem somewhat long too, but I'll need to get some proper hardware to mount all that for fit. I'll probably just stick with standard trumpets for starters and then migrate to a more custom setup later.
Now that I am in this far, and the coolant is all drained out, I'll probably pull the engine soon, and start the engine bay disassembly, in anticipation of doing the floors. Currently waiting on some welding and blasting supplies.