assuming you completely removed the lower screw from the brass coupler which joins the upper and lower shift rods...2 possibilities for the lower unit not coming off that I can see..1. the lower shift rod is still being held < squeezed > by the brass connector...2. the driveshaft splines are stuck in the crankshaft. For the first, try prying open the slot in the connector so the lower shift rod will release. If the driveshaft is stuck in the crank, trying working some wooden or plastic wedges into the opening you have and see if you can wedge it off. Personally, I've taken a 2x4 the length of the av plate and, working side to side, front to back,and beaten the lower unit off. Should you try this method make certain you strike the 2x4 as close to the exhaust housing as you can as you will be running the risk of cracking the av plate. It was a last resort in my case. Good luck. Make certain to grease the drive shaft splines, no grease on the top of the d/s. when you reinsert the lower unit. There's also a groove at the top of the d/s for an o-ring. Make certain to put one on.
You may get lucky and only need to twist and jerk some on the lower unit for the d/s to come free..hope this is the case.
