1. Won't hurt to grease them. But not necessary.

2. Probably not enough room. Grease before with regular grease gun.

3. A Ford shop manual is your friend. Get one!

4. More low end torque, a smoother tone on the exhaust. No downside.

5. Make this question a separate topic. Use the search button too. You are not the first guy on this forum with the same goals and questions.

6. Underside color depended on which assembly plant and timeframe your car was built. Some were Red oxide primer. Others were "slop gray" which was a mix of leftover body paint. The exact color of this varied by day and you would need to color match your particular sample if authenticity is your goal. Semi gloss black would look good too. Your call. Body color underside was never done on a Mustang from the factory. On an overrestored car at BJ anything can be done.

 

I would start with one of these...

H pipe (from what I have read) has a more typical "muscle car sound", but the X pipe has more benefits for high horsepower applications. Very general rule of thumb is the H pipe for torque and the X pipe for HP. Here is a

Get the new suspension on and drive it . Wish my car was that close...lots of time to plan the next motor build.

Remember more cubes will give you more torque and hp while giving you better street manners, so once you start planning think "stroker". If you are rebuilding the whole thing you put a storker kit in there, gain an extra 45 cubes, which will then need the better flowing heads.

 

Brrrr......20 degrees here this morning...hard to work on my 67 coupe in unheated garage.
16°F here.

Just got some parts in for my first mustang project - New leafs, 3.40 Trak lok rear, new axle brake lines, UCA and LCA, 1" sway bar, shocks, coil springs and misc........... Have a few questions:
1) Should I grease leaf bushings before install and if so with what? I have some 3M silicone grease - kind used for O rings and stuff
They should have nylon bushings between, no need.

2) Upper control arms came with straight zerk fittings- Will there be enough room to grease them after install if I change them to 90 degree zerks- Should they be greased before install? Just regular grease gun grease?- Planning on Shelby drop
You'll want to swap them for the special Mustang 90° zerks, to be sure you can connect properly. Ordinary chassis grease.

http://www.mustangbarn.com/PDFs/ArningShelby Suspension Drop.pdf

3) Anyone have torque specs on axle U bolts, leaf eye bolts, UCA and LCA bolts, etc?
The Ford Shop Manual.

4) Looking ahead at exhaust- plan on running duals with headers- whats the purpose of H pipe or X pipe?
The H pipe equalizes the exhaust pulses between L&R, reducing pressure and giving you 5-15 hp depending on other factors. The X pipe is similar, but works at higher rpm. How fast you drive, and rear axle ratio governs choice.

5) Looking ahead on engine rebuild- 302 '73 block - wanting mild cam, new 4 bbl intake, heads? Any thoughts? Want something mild but responsive, maybe 9.5 CR, something with a little lope would be nice- running 3.40 rear with 3 speed manual. Any Thoughts???? Would stock heads suffice or just as cheap for new aluminum? Don't under stand all the flow numbers I've seem 165cfm, 185, 195????
Use a C9OZ-6250-C hydraulic cam. Don't spend $1000+ on new heads unless yours are trashed, just port-match the iron heads.

http://www.mustangbarn.com/PDFs/Port Matching.pdf

6) Planning on cleaning and painting underside before commencing work - chassis black usually the norm? Saw the barrett jackson auction recently- they all seemed to be color matched with exterior colors...........
Depends on year and factory, but semigloss red primer is typical.

7) Any thoughts on anything else for a nice build? Just a weekend driver and cruise.
Sounds like a good start.