I am building a '49 Chrysler and also retaining the original flathead and fluid drive.
As for the front end, a close look and you will see it is only slightly different from anything you would sub in. Kingpins are there instead of ball joints and that's about it.
Parts for rebuilding the front end are readily available.
There are 3-4 VERY good disc brake kits available. The one I am using is from www.rustyhope.com
A shock absorber relocation kit from Mr. Street Rod will relocate the upper shock mount to the frame where it will be much more effective.
Some scouting wrecking yards should turn up a beefier stabilizer bar to replace the stock one.
Ply-Do, as mentioned, has a very good R & P kit.
Do all that and you will have as good a front end as a swap would give you at a fraction of the cost and work and you have an uncut frame.
There are a few guys at www.P15-D24.com
on the forum, who have done all of the above and more than willing to share their Mopar experiences.
Ask your question there and you will get more than a bit of useful info.
Article from R&C on a '51 Plymouth. Suspension is the same except for the steering knuckle(spindle). I have replaced the knuckle on my '49 with a Plymouth knuckle.