Do not use a ZF if you want a low first gear. The NV would be a better choice. Or even better yet
https://tremec-blog.com/tremec-tr-4050-off-road-manual-transmission-solution/I also have a Advance Adapters Road Ranger (older one) but mated to an NP435, a T18 would be even nicer. This was originally slated for my 77 dually for better towing and an OD but ended up in my 50 F1 since it was so low geared (4.27) and I didn't want to change the rear axle at the time. Plus I thought twin sticks would be cool (and it is). Some people can't believe it and really like it and ask good questions and then a few try and act like they know all about them and its super common cuz there uncles brothers cousin had a Mack truck that way... I just smile and say "ya same thing"
I have no complaints its kinda fun to drive actually, easy to shift, straight forward or straight back but as Frozen Merc mentioned you don't always even shift it. I usually start in the high side shift as normal 1,2,3 then low side 4th, then over. That's where the unit really shines is being able to split the massive 3-4 gear split of the original truck 4 speeds. It does have a little bit of gear whine but it doesn't bother me. Plus I have no idea how many miles are on it as it was used out of a 70's F100 mated to a Perkins diesel, I suspect quite a few. I did replace the input bearing and retainer as they where smoked.
You would end up with better gear selection for towing which is what these where originally intended for, old school hot shot trucks or trucks with big slide in campers. They also work with 4x4 trucks while using 4x4 since its before the trans.
In a 2wd truck it would be a fairly easy install. Probably easier than using a different trans anyway. No clutch or clutch linkage modification, original speedo will work (may need a longer cable) just new mount, shorter driveshaft and new holes in the floor for the shifters.
Definitely old school but I think they still have there place. On a side note I inquired to AA about the strength if I wanted to mate it to a toploader (they are rated at 420ftlb continuous) and do a little drag racing. Of course they can't give any guaranties or anything for liability reasons but he did say (and very confidently I add) I would be breaking toploaders long before I need to worry about the OD.