Being well over $7000 into a sub $5000 car (and not even having it on the road yet), the best advise I can give (that is not going to get listened to, I know) is you buy a finished car, not a fixer-upper. You will spend a WHOLE LOT less and the theory you will only need to make minor mods to bring it where you want. Cheap fixer-uppers are NOT cheap. I would almost say finance a finished car, as long as it's not going to be a race or track car. You don't have to come up with all the money at once, you are paying for your dream car over time and you get some equity when you are done. I am guessing banks won't do an auto loan on a classic car, but a personal loan would work.
Sounds like you already have things to tinker with, another project will only make them all take longer. I know, I've been in that boat. If it's a dream car, and you can find a way to purchase one that's done, do it. I know that sounds like wierd advise, but if I was the type to want a garage queen, weekend car, that's what I would do. I know that I can't really save $5000 in 18 months, but in the last year and a half I have spent well over that on my car. And like I said, it's not even on the road or ready to race.