The front and rear knobs on my t-54 look like this:
The front knobs are 29 mm in diameter, and the rear knobs are 29.5 mm dia. at the skirt. The front knobs are very dark brown. IIRC, the metal version of the set uses front knobs similar to those on the SW radios.
"The plate cap of the HV rectifier is awfully close to the lid of its box"
Do you have any shorter 1B3s? considerable variation in height can be found... also SS diode?
jr