Just to follow up for anyone it may help in the future...
I got the remote/throttle of ebay for £75. It was a second hand Mariner one, and by fluke had 12ft cables which should be fine. It will also link into the electrics on my engine with a plug which goes in the front. Not sure what this will do untill I try it, but it includes a kill switch. Just need to work out how to switch it over to go on my console.
The Steering was again of ebay. It was a cheapy Multiflex system with wheel, cable and bezel for £85. I will post back if this turns out to be duff.
I got the engine to throttle cables connections of ebay again for £38. This was a Yamaha kit, as mine is derived from a Mariner.
I also needed what I now know to be called a drag link. This connects the thru tube cable to my power head. This was about £15, I'll let you guess where from
It will be mounted on sometrhing I have designed myself and am getting a fabricator to make for me. It is roughly speaking a box which will be bolted to the floor. When I get it back I will post some pictures.
Thanks for all the help, hopefully this thread will help someone else as daft as me in the future,