I remember reverse thrust being fairly effective on the mk2 that friends had.
As you say, reverse wouldn't be much needed or much use in shallow, gravelly rivers etc, so understand why it wasn't much of a concern with the earlier ones.
You're right about the sound, certainly not an unpleasant one either. I always used to like it.
As for drawings, I have now found a side view and have a lead on a plan drawing which I am hoping will come good.
My only concern is that I've never built from a plan before, not a hull anyway and certainly not from an original view plan.
I will give it a go as and when time allows (assuming the lead on a plan is a good one). For now, I have more than enough to get on with, with my new to me, Sea Rover and Sea Commander repairs/refurb.