With a modest HP setup you cant beat a 700r4, only issue with them is setting up the TV cable correctly. Once that is done you are good to go. The OD and steeper first gear are both advantages, especially the OD on the highway even with a lower numeric rear gear. Keeping the RPM down is the secret to good gas mileage. The ones I use are from 1987-1992 F bodies, 2wd truck would be similar but probably different valve body calibrations. The 87 up 700s have the factory upgrades and you can identify them by the large MD8 cast into the side of the bellhousing. I run one in my 37 Buick now from an 87 trans am.
I used to always run TH350s in the 1980s and 1990s even behind my BB chevy engines. I always install a B/M transpak on level II and never blew one up, but depending on how tall your rear tires are a 3:08 was about as steep a gear I would run with one on the highway just to keep the gas bill down. I used to run with 3:55s and 3:73s, fun around town but not on the highway. I still have a couple on the shelf but once you have OD it is hard to switch back. With the 700 you can run a 4:11 rear gear no sweat.
Use a speed / gear ratio calculator to really find out what the truth is with your combination, I use it for every build. Plug in tire height and rear gear and you can see what your RPMs will be in each gear at any speed with or without OD. I shoot for 2000-2200 RPM at 60mph generally but I do hit the highway frequently.