Standard FSR-V rudder, you'll find various types at Ian's Boats (UK) , Prestwich (UK) , Hor racing (HK) and Evolution Racing (SE) to name a few.

This is my idea for a scale/ semi~performance drive setup... refer to picture. Also this would be a dual engine dual setup as seen in pic.

If you are going with a flex shaft then you do not need the angle on the prop shaft, run it parallel with the bottom. If you want to go hard shaft then they are also available from the links mentioned above. Problem can then be props as they mostly run 5mm threaded. There are of course ways around that.

68-70mm seems large for a submerged set up.

Ha yes very true, more like a 48-56mm right. Would this be better as a 3 or 4 blade prop?

pics of the hardware I was thinking about...

Who makes it?

I would not use a strut with a skeg with a
submerged rudder assembly. A rudder that close to a skeg would just fight itself not to mention cavitation problems.

i know its not ideal. but im looking for some scale-ish type hardware that can take the power in range of 25cc or 5hp;2lbs/ft. have you seen anything that would both look scale and hold this type of hp?

steve, check out the links at the top of page "4" i think HOR racing is where i found the ones i posted pics of...

Submerged prop boats have an extra measure of realism.

The strut you are considering is a good choice. Also consider the ones from
Marine Specialties:

www.marinespecialties-rc.com/

I have used his angled strut to push a 22 lbs Crackerbox with a CY F273 and
had no problems from the strut (100% thrust applied at the strut - floating
square drive at the clutch collet).

Dual rudders has an advantage as well. Certainly won't make the boat go
faster but makes pulling the flex shaft easy (no rudder in the way). It
is possible to maintain good control by running shorter duals and this can
help compensate for additional drag (compared to center mount single rudder).

If you want submerged prop to run as fast as possible then emulating what
the FSR-V racers do is worth considering. I cannot confirm the accuracy or
precision of the dimensions listed on this diagram.