If it is a solid coupler on the end of a tapered shaft, Comodave's puller technic may well work.
I would also be prepared to do the following:
- There may be a bolt, on center line of the shaft that pulls the coupler on to the shaft taper, remove the bolt.
- Tighten the pullers bolts only once, but get them reasonably tight, then after installing some fire protection blankets in the bilge under the coupler, using an oxy/acetylene torch with a heating tip (called a rosebud) heat the coupler quickly where it contacts the shaft. Don't heat the shaft itself.
Be prepared for the bang when the coupler releases its grip. Let the coupler cool naturally.
- Don't ever hit the coupler with a hammer unless you really want to buy a new one.
- Don't over tighten the puller's bolts or you could warp the flange of the coupler.
- Send the shaft out for an inspection/straightening and have the machine shop face the coupler when it is on the shaft.
Carefully reassemble with the shaft seal of your choice, maybe new shaft (cutless) bearings, a prop redo, align the engine/tranny to the coupler and things should be as smooth as silk, and dry!