but seriously the '68-'72 Mustang box can be laid on it's side for push/pull steering ...another idea is if the springs/axle are out of whack which they probably are now is the time to get nice and low because the frame arches up at the front to accomodate the parallel leaf suspension if you were to put a late '30's ford front crossmember and spring in after you straighten the rails you will gain most of that arch in drop ...
I'm not even gonna comment on the lack of pics after thumbing through three pages of posts... I will say though, why don't you put a hemi in it and be done with it?
Ok let's get this back on track. The 37 Plymouth has a very long engine bay and the steering box sits on top of the fram and stick out quite far to the left. A flathead ford is quite short. A tape measure will tell you that with the fan in the correct location the exhaust will probably going to need to snake around the exhaust. So pull the hood sides and run lakes headers. Or I have a rebuilt 37 Plymouth 201 with a dual carb intake, header and milled head for sale. Which will eat that fords lunch.