Well, what is the date on the back of your tach? Is it before October, 1970 or after? If before October, 1970, you will have to use a tach adapter or have the tach converted to work with the six-pin box. If after, you might get away with using the +5V TD output from the six-pin with the later version of the tach that used an +11V square wave. Worst case is you have to send it to be modified to North Hollywood, but get to keep the six-pin, so it looks like the original 3-pin and the car can be made to look original.
If you need a rev limiter you can get an aftermarket one such as the MSD 8278.
Why don't you just use an MSD box with a built in rev limiter and trigger off the magnetic trigger inputs? You may need either a tach adapter or to have your tach rebuilt to trigger off the MSD's duty cycle.
http://forums.pelicanparts.com/911-engine-rebuilding-forum/576337-msd-6al-how-wire.html
The magnetic trigger was a forward step vs. points. I think I would trade a Pertronix in the '74-77 distributor for a magnetic trigger, however. Can you find a Turbo distributor that rotates the right way?
http://forums.pelicanparts.com/911-engine-rebuilding-forum/303258-why-reverse-rotation-sc-distributors.html