You guys are also forgetting just how crazy the variables in just the engine blocks can be. There was that article in Mopar Action (i think?) where they weighed about 20 different big blocks; early and late 383's, 400's and 440's. There were lowdecks so thick they weighed as much as 440's and all those supposedly 'thin-wall' late 440's weighed up to 20lbs more than some earlier ones. By this account you could theoretically find a really light 383 block that weighed 30lbs less than a really thick 440 block. All were standard bore i believe.

Then you have the rest. I've weighed the intakes, even they can vary through the years... bigger/smaller carb bores, open plenums, different bosses possibly.

I've weighed about half a dozen cranks, all steel, and the 383 cranks weigh NO less than the 440 cranks... again, all standard. I was kinda shocked at this. The cast ones are lighter though... you could lose/gain weight there, but i've never weighed a cast crank, so i cant say how much.

I'd think the piston differences would be negligible. The longer rods, pushrods, etc. would be a couple pounds tops.

Thermoquad vs Holley is a noticeable difference, different air-cleaners could be as well... if we're sticking with stock stuff for comparison.

You could theoretically find a 383 thats 50lbs under the 440, or one thats pretty much the same weight... especially with the typical Mopar stacked tolerances... but i'd wager that if you weighed 1000 stock 440's and another 1000 stock 383's you'd end up around 20-30lbs difference.

We're kind of digressing from the OP's question.
The extra weight of the 440 (however much it is) is creating additional stress on the torsion bar crossmember. Likely, the 440 further aggravated an already existing condition. The extra weight has lowered the front end by the extra twist in the torsion bars themselves, PLUS the extra twist allowed by the tearing of the torsion bar crossmember itself. These two together have the effect of lowering the effective spring rate of the front end, making for sloppier handling - although possibly not noticeable.

1) Dialing up the t-bars to fix the ride height will solve, temporarily, any change in alignment. But the torsion bar crossmember will have to be repaired or replaced, before he finds himself driving home on his lower control arm bump stops.

2) Replacing the original bars is probably recommended, also, for two reasons. And I think most members here would concur. [1] Like any springs, bars wear out. After 40 years, his have probably outlived their usefulness. [2] The original bars are maybe .84, or perhaps .88 inches diameter. Going to at least .96 or maybe 1.00 will improve handling and still be a fairly comfortable ride.

Wow, it would help if someone who really knew what they were talking about piped up and put an end to all this speculation !!!

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Well, I crawled under the car today and found that the torsion bar cross member is starting to tear from the inside out right near the torsion bar socket. Must have just happened after the motor change.

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No way the motor change caused this. The motor is supported by the k- member and frame. The lower control arms are also supported by the k-member. The torsion bars tie the LCA's to the rear crossmeber BUT the only force that is exerted on the rear crossmber in the torsion bar area is "torsional" force - in other words, twist. Furthermore, those cars were built to take 440's and hemi's so look elsewhere for the cause - like maybe the floor is rotten.

If the frame, crossmember, etc is separating from the unibody there will be other signs as well ... there should be some distortion in the inner fenders or firewall and the gaps between the front fenders and doors should be inconsistent top to bottom.