Even though there's some work involved with the core support and such to bolt the fenders, grille, etc. back on in the correct position, how about using something like a Chevy S10 front frame clip swap. It would give you modern steering and brakes and there are kits to swap in a small block, headers, etc. and the track should be pretty close to the same as the '40. Also, I'm sure someone makes a crossmember that will weld or bolt in to mount a Mustang II system. In the rear, I might be thinkin' a 9-inch out of a Ford Bronco mounted on a set of leafs.

http://www.teufert.net/other/rear%20...dimensions.htm
http://www.eatonsprings.com/