going through hard times..have some questions, please help!

You just have to love cars, everything seems to go at once. Yes you can use your 78 tank on your 75. As for rims pick up a summit mag and take a look though it or call the tech line, they are usually pretty good at helping you get what you need.

I heard once that the '78 tanks were different, but haven't been able to confirm. I can't see why they would be. Do you have the plastic tank in your driver fender? If so it is another potential source of leaks. If you find that the '78 tank is different than the '75, let us know.

Even if the '78 tank is "rust free" you are very likely to find a bunch of junk in the bottom. I recommend having it cleaned and lined. If you want to do this yourself, the kit from Eastwood Restoration Supplies works pretty well. Here are a few pics of the '78 tank that I relined. Not perfect, but it won't have rust for a while. Just don't do it in hot weather like I did, and plan for more than 8 hours total.

http://www.geocities.com/m2cobra78/partspics2.html

Finding 4 on 4.25" pattern wheel with a small or no offset in the proper width is getting tougher all the time. Here are a few that I have been able to find:
http://www.eaglewheels.com/028.htm
http://www.eaglewheels.com/171.htm
http://www.eaglewheels.com/203.htm
http://www.eaglewheels.com/206.htm
http://www.primewheel.com/Primecatalog/pdetail.asp?model=261

Not all of these may be available.

And fitment may be a problem also...15"x7" with 4" backspacing and 0 offset may require some wheelwell adjustment. I would talk to a tire and wheel place before ordering.

Let us know what you decide.

Hey I just remembered I have an old set of "Chrome Keystone Klassics" for the II that could be refinished (paint the centers) You can have em for 50 bucks + you pay shipping.
they look like these...

You got a Pep Boys auto parts in your area? They always have a decent set of 'chrome' or even 'aluminum' wheels for the II for under $90 a wheel. Might have to order them, but they are still available. Eagle alloys makes a bunck as well as U.S. wheel.