Converting 33 recording to 78 how

I'm glad you know about different grooves and stylii. You're ahead of the crowd. Just to check, however, are you familiar with the different reproduction curves used in the preamps for 78 vs 33&1/3rd or are you transferring flat?

The way I've done it is to calculate the ratio between 78 and 33&1/3rd.

78/3 * 100 = 2.34.  So, you'll simply want to use that ratio when using the Edit > Interpret Sample Rate function. So if you recorded at a hardware sample rate of 44100 Hz, and the turntable was at 33.3 RPM then I'd enter in a sample rate of 44100 * 2.34 = 103194 Hz.  This will effectively speed up the recording, and we'll automatically resample to your playback sample rate (likely still at 44100 Hz).  However, it would be a good idea to resample to a common sample rate when you save the file. So you may want to perform Edit > Convert Sample Type and try whatever settings you wish and listen to it ​before ​saving to the new sample rate.