[techweenie]

The "cookbook" solution for that engine configuration is to use 2.7 S heads, which already have 36/37 (mine miked at 36.5mm) intakes. This is a better choice IMHO for an engine that is going to be driven on the street. For a pure track car, you might benefit from going bigger, but this is the ID used on the 2.7 RS engine, which was no slouch.

As for the front tub reinforcement, don't weld anything to a '71S chassis! The hood and bumper of a 911 just hang on the tub. The fenders do add some rigidity. It's likely you can find places to bolt an X-member in place to accomplish what you want, tying the front of the tub to the upper strut mounts with existing holes.

Again, if you keep the car from undergoing permanent changes, you will thank yourself later.

However, I must echo Erik's post: you'll be better off to do all this to a T.