I had bought the Gramodels warflat and ratio diamond frame bogies a year ago, and i fitted them with Hornby 3 hole disc wheels with peco tophat bearings, and so far have not come acrossed any difference in the hight or running with other wagons,
but i did scratch build a rake of 12 from the Gramodels 1,
all fitted with 3 link couplings, and yes they do look great with either Churchills or cromwells on them,( but i did for get to not put the side vents on ops!)
i will load up some pic`s for you to see what you think.
but they are in a nice BR green at the moment as i have run out of some paints,
Dan