Simon,

here are a few pics that might be helpful. What is your exact email adress(is it [email protected] ?I got a little confused by the adress in your post)I can send you some fotos of higher resolution there.
As for the strut, I opted for the straight axle option for cost reasons mainly (shaft and shaft tube were fabricated from stock rod and tube--->virtually zero cost). My motor (oh yes, it's a brushless now-can't wait to test it!) is placed about in the middle of the hull yet the strut angle isn't that shallow, which I assume costs speed. I just tried to keep the prop in relation to the stern as far to the rear and as below as indicated in the plans, but at a negative angle to the hull due to the non-flexible shaft. You could also exit a rigid shaft at the corner between hull bottom and stern, thus having more space to keep the angle shallow. In that case though the prop would be positioned too high and you would need extra shaft length to get the whole prop into the water when the boat is sitting.
If you plan to run a 540 with 6 cells, there's plenty of room at the extreme forward of the hull for the batts. If you make a quick C.G. check as per the plans you'll see that you need to keep the batteries in the very front portion of the hull to achieve the proposed C.G.
My construction is mainly 2,5mm balsa with 1,2-1,5 mm ply skins and is very strong without any glasscloth reinforcements. Maybe you would be adding too much weight by laying glassfibre over your structure...
The sponsons can be built out of thin ply and be filled with PU foam, a good flotation help on the one hand and you won't have to make them 100% water tight on the other hand(no cavities to get filled with water[8D]). The sponsons can be attached with hollow carbon fiber rods to the hull. A bit more expensive than aluminium rods but you'll always be certain they remain straight (ALU bends a great deal before breaking, while carbon fiber will either stay unbent as new or simply break-if you and 2 buddies step on the boat)

I'm by no means an expert on this field, so I would also appreciate some feedback on the strut issue myself from other people out there..

Be well, be fast!
Andreas