Looking at the following list, the 435 4 speed came in those trucks...seeing that, I would take a guess that if the transmission was built correctly and the rear end was a deep gear it would work...The C6 can take a pile of power even in stock form.
The last F700 we had, had an industrial 429 with a C6 backing it. Dunno if it was stock or a stouter trans than a light duty C6...but it handled 30k just fine.
Don't know, but I'd say probably yes. The problem is going to be the first gear, which is 2.46:1. Most of the 4/5 speed manuals that came in the F600 have a 6.00:1 ish 1st gear. with a low (5:1 or 6:1) rear end, which you may already have, I think it would be fine. But your top speed will be 45 - 55 mph.
One question that maybe needs to be asked, but what do you plan to do with the truck? IS it going to be used for that heavy of activity, or much lighter duty?
FYI if you do decide to use the C-6 Find the ribbed case.it is identified by 3 long ribs starting at the top of the bell housing & flowing into the case.these cases are much stouter than the smooth cases.I do know the econline vans of the late 70,s early to mid 80's series had them for sure.
We're building it for 9 passenger and it's going to be - more or less - old school hot rod styled.
That NP435 is so slow to change gear that I'm planning to change it to automatic and that's why I asked about C6. Okei there's also Allison AT540, but that ain't so common in Finland.
I know it is a little late but in my opinion if one is to use a C6 in any F600 then put as big of a cooler on there as you can get , also larger cooler lines !
For what it's worth, my folks had a 35' Eurocoach motor home on a John Deere chassis. It had an 18,000 lb GVW with all of the aerodynamics of a concrete block. It was powered by a 460 with a C-6 behind it. That drive train worked hard pushing that thing 65-70 MPH... The C-6 never gave an ounce of trouble....