We can run the engine up without the Bus, can't we? Someone must have a stand? Edit, I think you've made a valiant effort but like me, when I broke down last summer, you can get too close to the problem and another pair of eyes is what's needed.
Put it back in the bus, trailer it to TE and gamble that the great minds will crack it? I think it's a pretty safe bet that they would.
Drive it a few miles from home and break down, then recovery truck to Eddie’s. Worse case scenario the great minds can’t fix it and it has to stay there for a little while as @paulcalf ’s did a few years ago. But I bet it will leave better than it arrives. Worth a go?
Its better with the progressive to be very rich on a T4, as lean melts stuff fast, rich may wash oil off piston rings eventually. Eating plugs was probably a nice way of telling you the piston is next. If it was detonating then it gets hot enough to melt pistons. One way to tell is that your plugs get covered in a fine spray of aluminium dust from the pistons. The difference between very fast idle and very slow idle on a progressive is like 5 degrees of tweak on the throttle end stop screw. They act like they have an air leak when they havent. If the idle speed IS really fast, the centrifugal advance in the distributor totally messes up setting timing. You will get the effect where you decelerate, the revs hang high then suddenly drop. Basically as @zedders says, put points in it , static time to 8 degrees, LEAVE IT. Now get the throttle end stop and the mixture screw set so it actually does a lean best idle at 850 rpm. This will be iterative. Tweak one a bit, then the other. The high revs after a run is something I notice, I think on my carb its starting to wear out. A tap on the accelerator pedal makes it settle to lower RPM .