I just modified a fired case to make it work in the Hornady COL gauge. If you wish to do the same, I found the 5/16-36 tap to be the correct thread pitch and a 19/64" drill bit gave a nice pilot. Anyway.....
Did some playing around with the bullets I have on hand and found that the reamer (4D Reamer Rentals) we used on this rifle is almost ideal for the 360 North Fork. Lands are right around 3.392" with that bullet so no problem taking advantage of the whole Winchester length mag box. The 350 Hawks have to be seated shorter due to their shape (about 3.115" on average) but due to their much shorter bullet length 1.187" vs 1.395" they don't actually protrude into the powder space much more (about 0.045" if I did the math right). The cast also have to be short on OAL but still only go into the powder space a bit more than the NF.
Where the wheels fall off a bit is with the 400 grainers. A 400 grain Round Tip Hawk hits the lands at about 3.125" COL and a 400 grain FN LBT cast at around 2.8". They are both ending up way down in the case. If you plan on a .400 build and want to maximize the cartridge for 400 grainers I would recommend getting a throating reamer to set it up for the bullets you want.
For me, I think the 360 North Fork is going to be my be-all-end-all bullet for game and the Hawk is cheap enough for practice at comparable velocities and POI. I may still play with some powder combos to see if I see much change in accuracy/velocity. However, for all intents and purposes, Mainer's suggestion of a stiff load of RL 10x under the 360 NF gets me all the velocity and accuracy I need for 200 yard hunting (it hits 1800 FPS right around the 200 yard mark). That level of performance matches the original intent of the build. I do plan to do some expansion tests at 250 and 300 yards just for giggles and on the odd chance my dream moose is standing at 201.5 yards instead of 199.
When I get serious about flinging 400s I have a .416 barrel blank here and will just build a .416 Ruger. That is a significant and easy step up and will keep Mainer from being disappointed with all the "hobbiest B.S." as I think he put it so eloquently once Actually he will still probably get excited because the factory Ruger .416 rifle is the easy button. Unfortunately, they are also dang hard to find and north of $2K when you do (I just sold one well north of that and the buyer was happy to get it).
The only thing I have left to do is get the open sights regulated to match my hunting load and this project will be officially put to bed. The rifle does string a bit which I believe to be due to some flex in the forend creating contact. I should probably open the barrel channel a bit but fit is so nice as-is I hate to mess with the aesthetics for a nominal and unnecessary accuracy improvement (my notes show the NF around 1"-1.5" and the Hawks at 1.5"-2".
Actually he will still probably get excited because the factory Ruger .416 rifle is the easy button. Unfortunately, they are also dang hard to find and north of $2K when you do (I just sold one well north of that and the buyer was happy to get it). 
