07-23-2015, 08:56 AM
A 91B cabinet is too small. The 17B cabinet is about one half inch wider than the 91B cabinet. The 17 chassis might actually slide into a 91 cabinet but it would block the ventilation holes in the end of the chassis. Also, the 17 cabinet has ventilation holes drilled in the bottom. The best option might be a reproduction cabinet. 
Steve
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Steve
M R Radios C M Tubes