Starting to explore ideas for future drivetrain in my 68 F-100 4x4. Currently has a 360 FE with the NP435 and Dana 21 transfer case. This is nothing that is going to happen soon, I'm just trying to shore up some plans.

Currently torn on which direction to go on the engine. Not looking to make a decision on that right now, but I've narrowed it down to two potentials. First is to rebuild the FE into something bigger. Kind of want to keep it old school in a way although the engine would be modernized with a EFI system (already is). Second option is a 7.3 Godzilla swap, this keeps a similar sized engine to what I'd build as a FE stroker, but modern reliability and effeciency as well as long term (and easy) parts availability. Not looking to make a decision on that right now, but either route I take I will be looking for a manual transmission overdrive and two speed manual transfer case to use with them.

Problem is I'd like to select a transmission that can be used with either engine choice and to start collecting parts before I decide on an engine. Ya know the idea, spread out spending and be prepared to take advantage of deals and opportunities.

NV4500 and appropriate transfer case would be an easy choice for the FE, but doesn't exactly seem to be a great choice for the 7.3L.

I'm liking the idea of a ZF6 transmission like is in my 2003 F-250 7.3L. Would be a neat package with manual transmission, manual transfer case, and required shifter linkages and mounts. I'm not aware of any adapters to use it behind the FE, and probably not for the Godzilla either.

My understanding is that the 7.3 Godzilla uses the modular motor bellhousing. If I'm not mistaken the 6.8 V10 also uses that bellhousing and it came with a version of the ZF6, so that could potentially bolt to the Godzilla with the right flywheel and clutch selection.

I've seen FE to modular transmission adapters offered by companies like Speed Gems. So it's looking like a 4x4 6.8L ZF6 (if it exists) could check all marks. Usable behind both engines, manual transmission, manual 2 speed transfer case.

So is there any reason that the 6.8L ZF6 couldn't/shouldn't be used behind an FE?

Is there another valid option that could be used behind both engines? It's got to be manual overdrive transmission and have a manual two-speed transfer case available, preferibly with a transfer case shifter linkage that mounts to the transmission for ease of installation and adaptation.