Crank pulley drive - need an opinion.

Hi Guys
I have a badly stuck Massey 1155 V8 Perkins engine. I managed to get a good used one from a combine locally and intend changing the two over. Both engines are now out and sitting on my workshop floor beside the tractor. I have started to change over the simple things like oil pan, drive pulleys etc. My current problem lies with the bottom pulley attached to the end of the crank. The tractor has this attached by a splined mechanisim witha split cone and centre fixing bolt. This drives the water pump by vee belts. The hydrolic pump bolts onto the front of the crank with 4 fairly small bolts which is all fine.
The combine on the other hand has a different bottom pulley which is held with a woodrift key (fairly small) and three bolts into the end of the crank. I could have the combine pulley machined to provide drive to the hydrolic pump but it has been suggested that the three bolts and the woodrift key may not be capable of sustaining drive to the hydrolic pump. I will be using the tractor with a 4 furrow reversible plough (over one ton) mounted on the 3 pnt. I assume if the pump drive gives out then I lose brakes, 3 pnt and steering, not nice.
Anyway what are your thoughts? Has anyone had this problem in the past? Any ideas on how to overcome this other that striping both motors and changing the cranks over (lots of work).
Any ideas of thoughts appreciated.
Thnaks
Bill