I pulled a set of 6-leaf springs out of a 340 duster, but the drivers side rear hanger was shimmed, had a good 1/4" or more worth of spacers between the hanger and body. The car may have been hit before in the front and the frame dammaged, perhaps this was a way to accomodate for that so it would align properly?

What I'm worried about is the rear end housing - 8 3/4" unit. I'm hoping it didn't twist or warp when/if the car did get smacked around some. Is there any way you guys know of to check the axles/housing for any dammage? I suppose one spring just may be a bit weaker and sagged sooner then the other, hence the need for shims. I'm praying that axle housing is ok!

I once saw an article where a rear was gutted and the housing loaded into a large lathe. It was spun slowly with a dial gauge used to check for run-out. I don't recall what was done to corect it, but it might have just been put in a press and tweaked. I guess warped housings are not uncommon just due to the axle supporting the weight of a car for decades. Anyway, a true housing is pretty important to axle bearing life, etc. Otherwise, things start binding. Just like a bent crankshaft.

The shop that rebuilt my 3-rd member said he can check the housing for straightness for another $40. Just curious what he does to do so. Guess it would be a worth the pain to haul the housing over to the shop

Rear end housing straightness and how it sits in the chassis is important.
You rearend shop can check the housing, a small run-out error is not work fixing for a street car.

Rear-end placement in the chassis can be checked on a good front-end alignment rack. All of the newer racks can check all four wheels and yes, a good tech can tell you where movement (shims) are needed to get every wheel positioned evenly at all 4 corners.
With an A-Body, there is a good amount of adjustment in the front suspension but the rearend assembly is "fixed" and you have to get pretty creative to correct poorly positioned rear axle assemblies. The leaf springs are the "positioning devices" so look at the front segment carefully before adding shims to other places.
DD

Dr. Dodge is right. I'm a mechanic, and do alignments all the time. Go to a reputable shop and tell them your concerns. If your worried about the rear axle alignment being incorrect you must tell them. If you don't they will only do a 2 wheel thrust alignment (as not to waste time) because the rear of most rear wheel drive vehicles is not adjustable. So ask for a 4 wheel alignment and it will be really easy to tell.

Good Luck

Well since I was pondering getting an alignment anyway, I may as well put it on the car and have it aligned instead of going to a shop first to have the housing checked for another $40, then aligning it after words. I'd rather shim up leaf springs then go running around trying to find a decently priced A body 8 3/4 housing.