I did post another reply, but for some reason it hasn't appeared.
Installing the heavy Lakewood and threading it up between the chassis rails is a pig of a job single handed. So I've been out and taken some measurements without installing it.
By measuring the face to face on the Lakewood, plus the thickness of the block-plate and then subtracting the distance from the front of the bearing to the block mating face and the distance from the gearbox face to the base of the spigot, I'm left with 5mm. So that seems to be OK.
The engine was built by Bill at SA and maybe he was just taking precautions.
Paul