The original Desoto frame (assuming it used a Mopar frame in 1950) was a very good piece for 1950. The suspension and brakes were the best available at that time. ride quality in the 50s was all about soft and smooth, which these cars were. Soft also means softer cornering and braking. Better handling can be had with the addition of a better sway bar (if one is even present) and a simple upper shock mount relocation.
The frame can be converted to disc brakes, and a rack & pinion can be added (I suggest a Cavalier rack) and would be a must if you need power steering. The V8 will install (offset to the right 1 1/2" - 2") with mounts that are pretty simple to make. You may have to add a notch in the frame crossmember to clear the belt pulleys, it allows a lower motor installation. You will also need to build a trans crossmember, again, not too complex. The nice thing about using the original frame is it was made for the car, and everything bolts onto it and matches up. Front suspension parts are still available and may be as near as your local parts house.
The suggested Dakota clip (1988 through 1996) is getting pretty old. Around here, finding frame rails that are not rusting bad is getting difficult. This era Dakota can be converted to a 5 lug on 4 1/2" pattern (88-90 were 5 lug trucks, 91-96 were 6 lug trucks) that matches the rear end bolt pattern in your car (I would suggest you consider installing a newer rear axle as well).
The 97 through 2001 (or whenever Dodge revamped the Dakota again) has 6 lug wheels that are very difficult to change to 5 lug. The Dakota 6 lug rear end should fit in your Desoto by relocating the spring pads.
If you swap to a Dakota clip, you will need to build a front radiator support, and probably have to modify the frame horns ahead of the crossmember. I've done 3 Dakota swaps, with all of them I moved the motor/trans (I shift everything) back 5" on the Dakota frame, but none of my swaps were into newer then 48 model year cars or trucks. Shifting the motor & trans back gave me much better alignment with the wheels in the wheel openings, and set the motor in a better location for matching up with the firewall.
Cost wise, a front suspension rebuild will cost about the same money. Adding the rack & pinion to the original frame will add that cost. Upgrading to disc brakes will likely be cheaper then rebuilding the original front drum brakes. You will still have to deal with the rear original drum brakes, or step up to a modern rear axle and rebuild those brakes, both will bee about the same money, if your careful sourcing out a modern rear axle. Gene
