I took my engine mock up down to a dealer and plopped it into a 6.4 truck, minus the engine.
Generally, the engine appears to fit quite well.
There appears to be a height clearance issue in the front.
The mock engine models the 6.7 with the full valve cover. It appears that it might be possible to make the engine fit with the stock cover, but that it would fit better with a modified valve cover.
It also appears that it might be necessary to move the stock steering damper and possibly make a small change to the cross member.
The mock engine is a bit crude in the area of the front oil pan, in that it resembles the deepest part of the pan at both edges, whereas the pan on the real engine is only that deep in the center and the edges are shallower.
As the mock engine sits now, one could gain about an inch of clearance by contouring the driver's side of the crossmember to the shape of the pan. However, the crossmember shape may be just fine with the real engine.
Something will probably have to be done with the placement of the steering damper mount.
The length looks fine, but just. The mock engine contacts the 5R110 transmission face way before it contacts the firewall. Should radiator clearance in the front be an issue, the transmission my have to be moved rearward by a inch or more.
There is lots of room on the sides, especially in the heater box area. More so than with my '99. The amount of room is very impressive in this regard.
The stock engine mounts are very far rearward on the truck. They roughly align with the rear engine mount holes in the 6.7. It may be possible to use the stock Ford engine mounts.
It also appears that it is possible to insert the 6.7 into the truck without lifting the cab. But only just so. To do do, one drops the front of the engine down to get the oil pan sump behind the cross member and then lifts it up.
I think it is impossible to insert the engine with the transmission attached.