You're going to find a SM465 you're best choice for your application.
Read this - Adapting Ford Transmissions to GM Engines
Yes, it's possible to bolt a Ford T18 to a GM bellhousing, but it requires bellhouing machining, some transmission case modifications, and you'll still need to get an adapter for the transfer case. Those costs add up.
SM465 is a GM 4 speed, pretty much the same as a T18. It's a four speed with granny low and PTO ports on both sides of the case.
SM465 Ratios: 6.5, 3.6, 1.6, 1:1 Direct
Since the Muncie SM465 is a GM transmission, it will bolt up directly to your bellhousing...totally eliminating extra machine-shop expenses. They're cheap, plentiful, and really strong. You'll find them in Chevy and GM trucks from the 70's through the 90's. The GM Muncie SM465 Transmission - Novak Conversions
Is the 454 going into the '79 listed under your name?
If so, you've got a Dana 20 right now.
Now is the time to decide if you want to keep the Dana 20 or get a Dana 300. I have experience with both transfer cases in my Jeeps. The big differences inclue shifting, length, and low range.
Dana 20 "can" be a bear to shift (learn to finesse and you'll get over that though), it is shorter than the Dana 300 (better driveshaft angles), but only has a 2:1 low range.
Dana 300 is a LOT easier to shift, is longer (creating steeper driveshaft angles), has a desirable 2.6 low range, and has a lot more aftermarket support.
Strength wise, I'm not sure which is better. But, they'll both survive behind big block. Axles will snap before you encounter t-case issues.
SM465/Dana 20 adapter - Adapting the SM465 to Dana 18 & 20 Transfer Cases
SM465/Dana 300 adapter - Adapting the SM465 to the Jeep Dana 300 Transfer Case
If you can't tell....Novak has an EXCELLENT website