Well I'd start buy changing the 50+ year old leafs & strut rod bushings. Then start the search for ah, good, old, alignment shop that still knows how to work on old cars. And get that done. The lean could be do to several factors. But I'd start with the stuff you know needs replacement then go from there.

Shimming the front, if the problem originates in the rear, will just make your car start twisting itself and really mess things up.

How about a scientific approach?  What you need to do is to remove the rear springs from the equation.  Not from the car, just the equation.  Before you begin, measure the ride height of all four corners of the car, as measured from the center of the wheel to the inside of the wheelwell arch.  Write down those dimensions.

Find yourself a nice level garage floor or driveway, make sure all the air pressure is the same in the tires, and the front end is known to be aligned relatively within specs.  Then, jack up the rear of the car and put some jackstands on the pinch-weld lift points under the rear of the rocker panels (NOT under the axle).  Adjust the jackstands to equal height, being sure the rear end is held up with the tires off the ground about an inch.

Then take your new measurements on the front of the car, measuring from the wheelwell arch to the ground or, better yet, from the center of the wheel to that wheel arch.  Document the dimensions because they will be handy to have in the future.  If the front measurements are then equal, you know the rear springs are causing the problem.  If the front dimensions are off the same amount they were before, then you need to look at something up in the front.  If that is the case, then remove the jackstands and place them under the front framerail to repeat the procedure, but seeing if the rear wheels are equidistant below the quarter wheelwells.  That can tell you if the car is square, or if the suspension components are off, or something is bent.

I don't see how a strut rod could alter height, but spring perches can, and a loose upper control arm shaft can.  If you recently rebuilt the front end, and did not weld the UCA bushings to the UCA, one may have come loose.  Recently, an alignment jockey aligned my car and all the shims fell out of the right side.  I heard a pop and the car then sat 1/4" lower on that side.  Today's pressurized shocks can affect ride height a bit.  If one side lost pressure, it might sit a little lower.  Do not assume that new components are perfect.

I am betting the rear springs are the culprit, but it could be something else.  You just need to take measurements to see where the problem originates.