i don't know, ed.
as i recall it, as usual, the good minis were in canada and weren't exactly legal to import to the usa at the time. the safety conformation act of 1974 absolutely killed the mini in the states.
i was on acquisition missions as a young man and the 1250 cooper gts were not all that and a bag of chips!
you can't "heel and toe" a mini, their transmissons handgrenade and then, just for giggles, sir gilbert ever so cleverly built in the greatest planned obsolescense scheme ever devised - the crankcase and gearbox share the same lubricant
i'm pretty sure that you didn't willfully omit the saab sonett in that short list. my 1968 1500 cc V4 powered saab weighed in at 1275 lbs. wet could kick the snot outta' any of the cars you mentioned in alley rallyes and auto-x (back in the day we referred to those contests as gymkhanas,

what can i say? i'm a geezer!
with a bunch of hard core racing mods like trap door oil sumps, crank scrapers, oil cooling, weber dcohII carb, blah, blah, blah, you could get a mighty fine 200 ponies out of the old ford industrial motor without straining it. on the down side, you weren't going to pull that engine by hand (although as a young strapping buck, i would get a big buddy, a 2x4 and a chain and the 2 of us could muscle an engine with the transaxle out.) the v4 responded to tuning the same as a ford 289 small block, because it was essentially a 289 cut in half with the addition of a counter balance shaft and a european water pump.
also, don't discount the old vw beetle. although they were the epitome of a rust bucket, a ditch magnet, and a death trap there were an awful lot of porsche inspired go-fast goodies available through outfits like EICO for them.
i don't know if you would consider the corvair a light weight, but they were cheap and considerably spritely. i'll never forget the look on the face of the guy in the v8 nova after i spanked him roundly in my turbo'd horizontally opposed 6 cylinder "sleeper" spyder. i drove to toronto my first time with 3 other guys with that car and remember getting 3 speeding tickets on the new york tollway on the way home, the band "america" was playing "a horse with no name" on the am radio, the package of oreo cookies was open in the car for too long and the oreos tasted like gasoline, and we were tokin' up the last of the horrible crap we scored on young st! aaahhh, those were the days!
