One thing that may impact your choice would be your physical size. I am only 6'1" but something about my build makes me look & feel like somebody 6'4" when I get in a midget. It takes a special frame for me to fit safely in an older midget.

I can not get in an older 33" car without my kneecaps riding on top of the steering gear. I also can't drive an older 34" car (unless the cage is a plus 2" tall) without some sort of halo or extra hoop above me due to how close my helmet sits to the top of the cage.

I owned a 2001 standard narrow body Stealth 34" car and had to add a "luggage rack" to the top of the cage. It was basically the same size tubing as the main frame rails, bent and welded into the same shape as the entire top of the cage and it sat on 8 spuds that were 2 inches tall. It made the top of the cage 3 and a half inches higher which allowed me to have the seat high enough that my knees cleared the steering gear (by a half inch) and still have room above my head.

I'm not sure exactly what year the builders started building midgets with more cockpit room, but it seems that all the newer cars have taller cages and a bit more room between the A frame and steering gear than the cars from the early 2000s and previous. I sat in a 2008 standard spike and had more room than my older stealth had. The Boss chassis I have seen all seem to have MUCH bigger cockpits than normal. Most builders also offered and still offer cars with +2" cages but they are much harder to find used than standard cage cars.

If you are a smaller guy you won't need to worry about this with any car you find, but if you are taller than average or if your torso/leg ratio is different than normal it is for sure something to consider.

And most importantly....listen to the guys who have already commented...buy a complete roller instead of just a chassis. You will never be able to piece together an equal quality car as cheap as you can buy a roller no matter how hard you comb through ebay and classifieds. And even if you do find a sweet deal on a chassis, then a rearend, then a steering gear, then a tank, then a front end, etc etc you will end up getting nickel and dimed to death and spend twice as much time piecing a car together...not to mention the money you waste on parts that turn out to not be compatible with your car.