I'm trying to get at the impeller on my 1957-WH6 (Mark 6 - Neutral clutch clone) but can't get the drive shaft housing loose. I've remove the slotted special screw at the front top of the housing, the stress bolt and nut on the side and loosened the shift cable. The book says the housing should now slide off - not on this motor! I've tried to coax it with a dead blow hammer, turned it upside down and shot a liberal amount of PB Blaster into the housing - enough to see it run out at the power head with the motor upside down waited a few days, more Blaster, more blows, etc. I suspect the drive shaft is frozen to the crank shaft but can't see how to apply any other force to get it loose.
The lower driveshaft housing was finally removed by inserting increasingly larger shim material (flat metal, starting with a putty knife) between the upper and lower housings. Keep the movement even, balancing the size of the shims evenly around the housing. As suspected the driveshaft splines were heavily corroded.