TrevorK
I have a '70 Chevelle/Malibu 350. It started out as a VERY original car with a 2bbl. I dumped the 2bble and intake for a 4bbl edlebrock 650 and a performer. I have also changed to a dual exhaust and 15 inch wheels with 245/60's on front and back.
The car is in EXCELLENT shape (body/paint and otherwise) and the best thing is that it only cost me $6000! This thing is absolutely solid and has actually won a few local shows.
I have had the engine out a few times for cleaning/painting (which is when you REALLY learn about your car).
I have to say that you should get as close to original as you can and stick with GM/Chevelles as they are the easiest to find parts for at a decent price. Plus....you can put ANYTHING in a chevelle!!! If you have never owned or driven a muscle car then a 350 is a great starting point. Plenty of power to start and VERY easy to build up to the next level.
Try to get a car that has a solid body with good paint. NO BONDO or RUST unless you are a body man or know someone who can do the work for you for a good price. You will spend the most money on a pro-paintjob/bodywork than on anything else ($4000-5000 for a basecoat/clearcoat with minimal bodywork).
Most importantly....find a car you LIKE...don't settle for something because it's a good price. You don't want to sink large amounts of money into something that you really don't like.
Here's my site
Muck's Place
http://members.tripod.com/nvmymalibu/id29.htm
The top '69 Camaro is my Dad's, the '66 Chevelle is a joint venture between my Dad and I, and the '70 Chevelle is mine. I am currently building up this site so don't laugh

. Click on the Camaro and you will see a detailed list ot the things my Dad and I have done to restore it (pictures galore so I hope you have broadband

). This is an extreme case of RESTORING to ORIGINAL. A LOT of money was put into it to take it back to showroom perfect!!!
Our next project is the '66. It is currently stripped down the the shell and is now in the 'shop' getting painted Marina Blue (I LOVE that color)! We aren't going for the ORGINAL look on this one but man will it be sweet!
The last project is the '70....I'm leaning towards the Baldwin Motion look with either Red/black or Yellow/Black......
Hope this helps....
SDC