Actually, you don't need to do much of anything.
I have been to SVRA vintage events here on the east coast, where the only "mod" to the car was tape on the headlights.
And, although "history" is nice, it is virtually never required. I have seen ordinarly Minis painted up in replica-livery of the BMC works Monte Carlo cars....lots of other similar "replicas". While this might be viewed as "fake history", it is usually fine.
Many vintage clubs, including VRG (the vintage club I have run with) will allow the driver to sign a "roll bar waiver" if the car is not so equipped. I have seen SVRA races where some of the cars did not have seat belts or roll bars.
I guess the logic is that many owners not wish to modify their valuable classic, even in the name of safety.
I'm not saying *I* would race a car with no roll bar or belts, but it is not uncommon in vintage racing.
Virtually all vintage clubs have a "13/13" rule, which essentially bans a driver for 13 months of racing if they are involved in *any* metal-to-metal contact with another car. This rule tends to keep the cars "spaced out" more than a regular SCCA-type club race and it is particularly obvious in races with pre-war cars (probably because they are much more valuable). And pre-war cars almost always run in a separate race-groups from newer cars.
One of the most important safety features in vintage racing is not in the car but in the driver's head. There is great respect (and even reverence) for certain cars. And most of the drivers are in it for the fun, and do not care about winning another $10 bowling tophy.
Last year at Summit Point, I was able to have a nice 20 lap "dice" with a Sebring Sprite that was formerly owned by Graham Hill. I will never forget that. If you try vintage racing, you'll be hooked!
The *big* thing to consider is whether or not you could "write off" the car if you really screw up. This is always a possibility in racing and it can have a lot to do with how much financial pain you can bear. I have seen Lulu Wang race Hammer-n-Tongs around Lime Rock in a Ferrari GTO that her husband payed 6 million dollars for. Guys like me would have a tough time writing off a common Sprite (which is why I'm switching to a cheezy Ford Escort for most of my non-vintage club racng in '07).
I am including a link (below)to the VRG Rules and Regs. These rules are very similar to most of the other vintage clubs that I am familiar with. You will see a lot of "recommended" (but not required) terms, as well as "waiver allowed".
Rules&Regs Link:
https://www.vrgonline.org/rules®s.htm
By the way, the big "schism" in the vintage community seems to be "How old is a car before it is truly vintage?".
Some clubs like the VSCCA (
https://www.vscca.org ) do not allow any cars newer than 1959. Further, if you have a fairly common, older car (such as a 1958 MGA), you may have to go on waiting list to run with them since they prefer to have a nice mix of cars and they already have plenty of MGAs.
Other vintage clubs such as the HSR (
https://www.hsrrace.com/ ) have been roundly critisized because they allow too many "moderns" racing.
Clubs like VRG (
https://www.vrgonline.org/ ) suggest that cars be built before 1972. My car (which is really a 1978 MG Midget) is allowed to run because it has been "backdated" in appearance.
G'luck! If you try it, you'll love it!