I think 6800 is the light GVW F-250 4x4 with the 44 front end and semi float sterling rear. The frame, springs, axles, etc will handle the power and weight just fine. These trucks had IDI's in them that weigh considerably more than the 4BT.
My only concern is what transmission it has. It's either the M5R2 or ZF. If it has the mazda tranny and you plan to really abuse it you might break it.
If I understand correctly, a 4bt from a "Ford" bread truck (assuming it was OE with a 300 six) will fit without too much trouble. I can buy this 91 truck at a fairly reasonable price, and figure it would be a better start than my 87 with a 460 and T-19.
My concern was that the front springs/diff look substantially lighter than my 460 truck (8600 GVW). I have limited facilities/ability for fabrication and as such have reservations about conversion of the 460 truck, as it would likely need something besides the T-19 with the 3.55 diffs, and who knows what else for motor mounts.
Ford had two differnt F-250 TTB front axles. The TTB44 and the TTB50. The 50 was used under the heavy GVW F-250's, the 44 was used under all the light trucks. The TTB44 uses the light 1/2 ton hubs and spindles. The TTB50 uses D60 hubs spindles and stub shafts. The 50 is substantially beefier, but it still has the same gears.
The biggest benefit to the 50 is the hubs and brakes. Both axles use the same rotors, but the D50 and D60 use a different style caliper bracket. If you want to upgrade your front brakes you can swap in the heavy GVW F-350 super duty/F-450 calipers onto any D50 or D60.
I wouldn't let a TT44 stop me from buying a truck. You can buy a 50 for $50 and bolt it under.