If you can get time in a T-34, I think it can't hurt. Check out
this website and download the "Basic Instrument" (BI) Maneuvers FTI (Flight Training Instruction).
Like some other people have said, I'm sure the A handles a lot differently than the charlie model. As for the cockpit layout, you can get a good idea of the charlie's layout by looking
here. That's a screenshot from the Microsim add-on for flight simulator that the Navy provides to you during primary.
If your cockpit looks anything like that, then, in my opinion, doing the basic instrument maneuvers found in the Instrument FTI would help in building your scan. (Again, I'm unaware of your level of familiarity with the terms- scan is the method in which you obtain information from your instruments... basically which instruments you look at, in what order... all explained in the FTI)
One thing you definitely should not worry too much about GPS approaches... you probably won't do them in the T-34, and definitely not in the T-45, should you go that route. The -34C *does,* however, have a KLN-900 GPS system installed, so concievably they could change the instrument syllabus to include GPS approaches. I can't speak, however, on the T-6 primary syllabus, as I was a -34 guy... it is entirely possible that you would do GPS approaches should you fly the T-6 in primary, since they lack a TACAN. Personally, I have my wings and am headed to the Hornet rag having never shot a GPS approach.
Hope some/any of this helps... I think you have a decent opportunity to not really develop your skill, but develop a certain degree of comfort and familiarity with the -34 in an instrument environment, so that you are that much more comfortable when you are sitting in a Navy trainer.
Don't kill yourself, but success is the product of preparation. People might give you a hard time about it because things like this are seemingly small pieces of the puzzle. However, when you make these little efforts in different areas, and sacrifice little bits of your time on multiple things like this, they will add up to an overall better state of preparedness when the time comes.
Good luck, have fun, and good on you for finding a way to better prepare yourself. 90% of this stuff is motivation-driven prep work.