I try to finger all the 1st Gen's I can at the shows where ever I'm at to check them for side to side tire fitment.
I just put a couple of fingers right at the top of the tire corners and the middle of the wheel wells, both front and rear and side to side!
I've found through the years that our old cars can be off as much as two fingers one way or the other and its usually like a finger to maybe a finger and a half in the front and like two fingers in the rear OFFSET TOWARDS the pass side!
I know my car is this way and as far as I know it is a virgin chassis-wise.
This is why some cars will cut the tire corners at full droop and others won't, BUT only on one side!! Mine has done this so I figure my finger deal is darn close!
And another point is that years ago, my pass. side front coil spring sagged and I threw a fit and got the Area Zone Rep involved and he said, "Heck, +/- a 1/2" ground clearance was fine w/ GM" and I said BS and paid like $22/pr
for my 396 H-D, A/C springs that are up on the shelf now and GM installed them free!
Remember, this is WAY before electronic laser alignment crap that is around today.
Another deal is that guys make the front rim mistake of trying to install wider rims w/ the dish out towards the wheel well lip instead of deeper in!
My 7" wide front rims w/ 3.5" b/s and old E-60/14 tires put the outer tire corner out too much which caused on occasion, the wheel well lip to cut the tire!
Remember that stock front spacing on our old cars wheels is like for a 6" wide rim, 2.25"!!!!!! And stock BS is 3.75.
PS., and when I installed my bolt-on Jegs S/F/C's, I tried to shift my rearend over a bit to better center it using the STOCK front spring eye mount holes slop by wallowing the mount holes out just a schosh, then measuring side to side before I tightened everything down. I gained like 5/16" or so better centered fit!!
You will see what i mean IF you get this deep into her.