Been MIA for a while, but just checked in and saw this! Welcome to the paint shaker club! A 4BT is a different beast, but it's a lot of fun. I can haul my 6500 lb Land Cruiser's fat ass up anything at I get fuel economy in the low 20s on 37s and run it on biodiesel and vegetable oil to make myself feel better.
I don't have time to read the whole thread (I'll have to make time) but it looks like you're doing it right! Nice work! You'll be in good shape with the NV4500, although you might want to step up the tire size when you're done. I have an H55 (NV4500 is a better choice for a 4BT) and I have 3.73 gears, it finally was really right after I put it up on 37s, actually gained an MPG to two.