Re: Will these 650 lower units interchange? (pics included)
The preload pin is used on lower units that have a tapered roller bearing on the driveshaft. Other lower units using a 'straight' ball bearing do not require any kind of bearing preload.
There is another important difference between the two that you should be aware of, however: that O-ring groove in the old driveshaft that you don't see in the pic of the L/U with preload pin.
On older models the O-ring seals the driveshaft/crankshaft splines to keep them from rotting away or freezing together from corrosion.
So you're gonna want to grind a groove for an O-ring in the replacement. Or, pull the powerhead and press into the bottom of the crankshaft the seal assy that takes the place of an O-ring on the driveshaft.
Not that hard to grind the groove, I've done 'em by hand before with a grinder disk chucked-up in an electric drill. But an electric grinder or air motor would probably make quicker work of it.
If you don't do a groove, recommend taking the lower unit down a couple of times per season and re-greasing the splines, especially if you're running in salt or alkali water.
HTH...........ed
