K4 Space Required

The photo below shows a K4 unit face down requiring 210 mm to aft section of a 19.50"  blade. Allowing 220 mm to both cater for a larger 20.50" blade and also tolerances for measurement plus clearances to the rear is the minimum required for units that  mount flush with the taper big end.

NB:  SHAFT SIZES OF 40 mm  and SAE 1.500" require an additional 20 and 30 mm respectively as these units mount down the taper to preserve boss commonality as indicated above:

Below is an actual SAE 1.500" installation in an aperture showing the critical space requirements.