No dumb questions... no worries.

Yes, TH350 is short so to speak for a Turbo 350
and this will be the most direct replacement for the ST300 2 speed you may have now. Same driveshaft and yolk, cross member should work etc...

You'll have a different kick down set up (cable style)from the 2 speed (electric switch like the TH400), but that can be figured out later... no big deal.

Just make sure the replacement is a BOP (Buick/Olds/Pontiac) tranny, as they will be direct bolt ins, where a Chevy TH350 will have a different bolt patern....

Good luck, and I hope this helps some?

Brett - 67 Drop Top 455!