Quick update on this.
Tracked down tohatsu control box and steering link from eBay. Jamiegolf supplied crossbar steering (stamped 8ft cable), throttle, shift cables and all of the linkage bits and bobs, top man all as described and spot on.. Cable lengths are all bang on.
Quick trial on Saturday morning confirmed that my outboard was way too high with my current set up for tiller steering. Back to the garage to get transom back to original state.
Out today on Sunday and after testing various outboard heights using different blocks of wood and playing with the trim on the 25 2 stroke I found that I got the best results using the steering system with no extra outboard height and the outboard trimmed either all of the way out or second from last hole. Couldn't quite believe no engine splash over the transom! Think this shows just how critical the weight distribution is on the Aerotec.
It jumps up immediately on the plane but I did notice at wot that the steering seems a bit vague. This was a bit of a worry at first but I think this will actually be fine. How often do you need to do a full lock turn at wot? Slowing down slightly and I feel it digs in a lot better.
I have a bit more tweaking to do, moving fuel tank etc but overall very happy with the steering set up.