Thanks for all the input again gents. Much obliged
For now I'll be doing a few things first, now the boat is emptied out:
1) De Grease the inside and sand a lot of the surface smoother as it's full of horrible bits of additional resin slopped around it. There's a bracket by the end of the prop shaft/stuffing tube where it had some sort of RPM sensor I think but long gone now and not even sure how that would have been used in terms of recording info or relaying it to shore etc. So that's getting removed.
2) I'm going to add bouyancy in front of the engine where the tank currently is. It's a DuPro tank on a resin coated wooden cradle but it's an engine out job to access it, which I don't like. So it's getting moved (or replaced with a slightly smaller one) to go between engine and radio box. It'll affect balance less as it drains too, and will be easily accessed.
3) Maybe add an auto bailer or two to the transom. There's too much hole area open in the hatch for my liking, which will equate to a lot of water getting in I suspect, and if it gets in it needs to get out again. I've not read up on the efficacy of these though.
4) Adding an oil/grease nipple to the stuffing tube (ordered one from Prestwich)
5) Dig out a better servo for steering than what's in there and see what radio I will fit in it. I think I have a spare Spektrum 5 channel one sitting around not doing a lot so that might do.
6) Fit a proper cut out switch since it currently has a loose wire that you short to earth to stop the engine. I may attach a spare channel to this and add a failsafe (think I have a spare one), then I have two separate safety options.
7) Make some means of actually attaching the hatch to it since it currently just sits on top. No idea how it was previously secured. Some sort of pins & R clips arrangement presumably will do.
I'll have a look at the carb stack as I know it's beneficial to have it curl round but not sure how I really can with this since it's effectively a cone that's too thick to bend, but not really thick enough to turn down on the lathe to create a nice wide radius on the edge if you see what I mean. Not sure there's much I can do with it but we'll see. I won't mess with the carb itself for now as I want to see how it goes with the existing setup, then I have at least a visual benchmark for effectiveness of future upgrades. I can't really test it for speed without buying some sort of special GPS gizmo I don't think.
9) Add wheels & a handle to the stand, plus a strap to keep it secure.
10) Sharpen the prop.
11) Smooth off the resin on the tip of the bow as it looks really bad
12) It's tempting to add a channel that can raise & lower the angle of the prop so I can see how it behaves, and effectively trim it on the water for the conditions. Might be overkill though and a bit of hassle.I'll leave it as sub drive for now as it's been set up that way and obviously used that way so someone thought it was ok. Might not be the best thing, who knows, but I should try it first before potentially chopping stuff about to convert to surface drive, as I might be quite happy with how it goes.It did cross my mind that sticking a big brushless motor in these days may well give better performance with less hassle (as much as I love IC engines), without worrying about stalls/cutouts etc. But I suspect the combination of a decent motor, ESC, and massive battery might cost a bomb, so again, try it how it is first and see.