Great project. Good luck with the 6-BT. I was going to mount a 6.354 Perkins, which is nearly identical in size to the 5.9L, in my 46 Chevy 2-ton and it simply would not fit without hacking out nearly the entire firewall and having the back of the block under the dash. Heck, the 250 inline-6 gasser I ended up putting in is right up against the firewall with no fan on the front and I still had to relocate the radiator to the front of the core support. The 6-bt is a good deal longer than that little gasser. I'm not saying it's impossible to squeeze in a 6BT but it'll be intruding into an already small cab. If you have your heart set on a Cummins diesel, you may consider trying to find a 4BT out of a step van. That's what will be going in my '46 when I get the time to do the swap.
