Mr. Yuck -- You're on the right "track" to first be deciding what class/club to build your car upon. So many ppl will just build and modify... then later discover they're not built correctly to be competitive in a class/club they enter... result: unhappiness, $$$ wasted, and back to the drawing board.

For the w2w racing with an older car, I suggest picking up an issue of Grassroots Motorsports magazine, or else Vintage Racing (?name?) magazine... they have multiple clubs and series you can investigate... and determine best class/club rules, etc.

Here in the Midwest there is the Midwest Council of Sports Car Clubs... www.mcscc.org (see their rules on their web-site) that has w2w classes for older cars... "Vintage/Historic" which is where older cars run for fun... not super competitive.. but gentleman fun!.. and very attractive to the fans and fellow racers.

There must be some similar clubs in your area... ??? Local clubs tend to be more at-ease and forgiving on rules vs national clubs.

Keep it low-budget and you'll race more than repair.

For parking lot/autocross racing, typically the SCCA classes we can set up our older cars best fit in E/Street Prepared (E/SP), CAM-T (a recently developed class rapidly gaining popularity), C/Prepared (C/P)... all-out race GT-1 style, etc.

My own car is setup and maxed-out for the E/SP class rules (introduced mid-1980s by the SCCA... very competitive!). CAM-T is looking more attractive to me... more mods allowed than E/SP... but then more $$ to spend to be upper-end competitive... time and $$ is all it takes, as with everything.

Eventually, most older pony cars want-to-be C/Prepared (for SCCA pylon Solo racing) as its the ultimate pylon class for our cars... It CAN be relatively low cost.. but typically becomes very expensive... good class for creative craftsman!