Looking for advice!

I inherited my brother's '75 Formula 350. He started the resto process, interior, etc. Running gear is all original. I will continue it the job, but like him, I don't intend for the car to be a trailer queen. I m interested in upgrading suspension and other items without detracting from the body lines.

The car has the original B-W 4 speed, and I am considering swapping to T-56 6 speed. The car cruises well, sees almost 15 MPG with the rebuilt engine, but begs for lower cruising RPM at 70 and 75. Plus the bottom end punch is not as strong as would like it to be. There is no center console, the car had the standard interior.

So, for the swap, I have these questions:

1. Does the tunnel need to be re-cut to accommodate the shifter?
2. What about the transmission mount location?
3. Clutch and flywheel: do they need to swap out?
4. Does the drive shaft have to be changed/cut?

Any other thoughts/advice would be helpful., too.

Thanks!

Mike