Hi Dennis...I'm not sure about the TF series trucks but on an A.D. if you fit the under floor unit,you do have to modify the floor to access the m/c.(sorry I don't have pics,I've still to do this mod!) Only problem I've noticed is... it's under the seat frame on mine! headscratch
Certainly this does give you a cleaner firewall but it doesn't look too out of place in the engine compartment.
If you choose the firewall set-up you MUST reinforce the bulkhead though!
Jock. thumbs_up

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.