[TR] J vs D Type Overdrives

[Joao Simoes]

Hello, all.

As mentioned before, I am building a Spitfire bodied GT6, using a 73 GT6 chassis and running gear.

I have 2 questions:

1- The GT6 has a 3 rail trans that can be mated to a D type overdrive. I was told the J- type overdrive is stronger and was used on 74 and later Spitfires with the new, single rail, 'Marina' gearbox.
I happen to have both transmissions and was curious if I could adapt a J type overdrive to go on the 3 rail trans, or use the single rail on the GT6. Any tips?

2- I mentioned before I am also building the 2.0 liter inline 6 to be 'warmer', hoping for say 130 hp. Any recommendations on a cam and if I would need head work, better con rods, induction or exhaust improvements? 

Thanks for any wisdom you can impart. And also does anyone live near the Ann Arbor area?

Take care,

Joao