Not sure about the 7/8" ive only ever seen 3/4" or 1" motors. But have not seen much new stuff. Most are 3/4 and if i remember right the Ultima was a 1" shaft. Best wait till you get the boss.
A power Torque motor is around 2 1/4" (52mm) face to face. (a bit hard to measure free hand)
An old victa 4 stroke will have a 1 5/8" shaft (47mm) you gain about 5mm in the seat of the blade boss.
Older morrisons and masports 2 3/8" shaft (62mm) Later Victas also use this with a 15mm spacer ring.
Rovers, MTD and flymo etc 3 1/4 (81mm) (could be 3 5/32") so that would be a fairly high spacer.
Best thing would be to grab a couple of steel rulers and have a good measure when the crank boss turns up.
I would be aiming for the right shaft length, the longer it is the easier it will bend.
Those crappy 24" MTD slashers with the 3.75 sprint motors on them were only a 3/4" shaft x 81mm, ive seen a couple of bent ones. Seen some regular mowers with the longer shafts that were bent too.
