Ahhh a mid west car...we all know they never rust (except when they are 914's)
If the car runs and all it needs is a switch ( and you can do the body & paint ) then have at it and leave it stock. No need to cut up the other car and transplant non original parts on to it (stock cars go up in value faster than modified ones, unles they are certain race heritage cars)
As to the engine harness, there is a member in the Resource section of the board who can help you with the repair/replacement.
There was no Le Mans edition of these cars. There was a LE (Limited Edition) or a Can-Am edition. I'm not at home to post the links to the LE cars, but if you can post the serial number of the 74 someone will be able to tell if it's in the known production range of the LE cars.
The orange car, altho interesting, would need various modifcations to be street useable again. The front and rear treatmens look interesting, but not functional to be used as a street car or on a track with out some sort of bumpers.
If they were mine, I'd fix up the 74 and keep it stock. Then I'd fix up the 73 and drop a SBC in it. Nice truck BTW
Ah...there he is now...see the links in his sig for info on the LE cars