I think sliding the nylon tubing on is similar to what people deal with in modern gas car's fuel tubing, but a much larger OD. In gas cars, you submerge the end of the nylon tubing in boiling water (just the end), then quickly slide it over the metal barbed fitting. I like the idea of heating the metal fitting, especially if off the vehicle. If really stuck, the vacuum distribution is just a simple plumbing problem, so one could redesign much of it w/ parts from Home Depot.

When replacing rubber vacuum hoses in my 300D's, I use silicone hose since it lasts almost forever, and blue for bling. I have a few rolls of various sizes I use on all my cars. Ditto for silicone hose when replacing heater hoses. I even re-plumbed the Rube Goldberg heater tubing and hoses in my 1985 with silicone hose and aluminum tee, so need not worry about sourcing those special curved rubber hoses in the future.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans