Hmm...the messages with the 40 series 14" tires are almost 5 years old. The tire and wheel business has changed a lot in that time. Very few low or zero offset wheels are available in the 4x4.25" lug pattern anymore, in any diameter. And the tires that fit those wheels are slowly going out of production too. Mostly because the only cars with 13 or 14 inch wheels these days are very small FWD economy boxes. And 40 series 14" tires were not a high volume item even when they were available.
I looked at a lot of web sites such as BF Goodrich, National Tire and Battery, Discount Tire, etc. and found the TA Radial you wanted for the rear, but not the front. But you know that.
Tire Rack and Summit Racing have the best websites I found for tire searches as both will list all of the sizes available in one wheel diameter. Both had a number of 14" tires.
SummitRacing.com 14 inch tires
Tire Sizes by Diameter : Tire Rack
You might just have to figure out what difference in diameter you want in order to get your front-to-rear stagger and compare that to each tire. Maybe you can do it with both 60 series tires. Sorry I can't be more help. I think that these days most Hot Rod guys do stagger with wheel diameters, but unfortunately we're having trouble getting wheels in multiple diameters for our 4x4.25" lug pattern also.
Oddly enough, one of the tire stores in a 5 year old message early in this thread still lists a few zero offset 4x4.25 wheels:
14 inch custom wheels - RIMS-N-TIRES
Coker Tire lists the MII sizes, but don't have any available. Since we are entering "antique musclecar" status, maybe we can get them to make some!
Coker Tire*:1978 Mustang:*Search results