Ah, so the original post wasn't so much about a rig for YOU, as much as a product to build for customers. That puts a slightly different twist on it.
In any case, diesel cruiser engines aren't hard to get at all, Greg and Sheldon have a thing going in BC where Dave Stedman ships them over from Japan. Greg and Sheldon both plan on attending CM06 this year, along with a good sized contingent from BC.
I forgot to mention that in my plans for my 71 I'd like to EFI it...I know of a good number of people who've squirted 2Fs, but I've never heard of anyone doing an F!
On lockers, not only are 80 series electrics an option for 40s (you need custom length axle shafts made), but HJ61s were available with cable lockers from the factory. Gary Coberly from Lone Star has them on his, and I believe Peter Straub from Rocky Mountain has them in his too.
One of these days I'd like to see an H55F on the shop floor, side by side with an R151. Looking underneath, the H55F seems a LOT bigger and beefier than the R151. At about 5:1, combined with the low diesel torque, I never really felt the need for lower gears in my HZJ75, even turning 35s and dragging 7000 pounds of cruiser up the rocks.