"Shaft could turn easily in one direction and more difficult, but not impossible in the other." Since the problem only comes on with heat, I'm assuming it is leakage to the rear clutch apply at this point rather than a sprag issue, which I would think, should be evident all of the time.

The carb is a TQ from a '74 400, but the throttle pivot location is in the same as every production TQ I have or have seen. I am using a thick base gasket and am not going to use an additional spacer. The kd linkage is unknown. I'm assuming it is 4bbl since it lines up with the 4bbl carb, which is more outboard than 2bbl, but can't say for sure. I didn't love that bar lean either, but in all of my research I have seen it on others and assumed it was ok. Did they have lower KD linkages for 4bbls? The only difference I noticed was for single piece vs the bellcrank type. Both were used on trucks of this era seemingly with no rhyme or reason (at least to me). EDIT: Below is a 3,400 mile '78 LRT and another un-modified 360 4bbl same era. Note the bar positions