I don't know where you're located, but it would be a good idea to have someone knowledgeable about single-ended triode amps take a look at it before you start sticking tubes in it. As someone else mentioned, it could be intended for a 300b, a 2A3 or 45. At the very least, if you post a detailed photo of the underside, some of us may be able to identify the circuit and the possible tubes based on the obvious connections and component values.
Or maybe your dad only had some 300Bs, in which case that's probably what they were for. The trickier part is the input tube, it could be any number of 9-pin tubes. Don rarely stuck to one particular design.