For a non-step boat, having the prop a bit low gives the drive(s) leverage to carry the nose which lowers total drag more than the added drag of the lower mounted drive(s). So you could end up with better planing, midrange and top speed.

agreed... a small sacrifice to make in the larger picture of driveability... and yes Mild Thunder, the III, as it was intended by Mercury, was to be run below bottom, not above like a IV or V...
the way I rig these boats is usually in the area of 2.5" to 3" below if the engine location will allow for the high mounting... seems to give the best of all performance, planing ability good midrange and topend performance...

Is there a prop adaptor to run large shaft props on a small shaft? What others props will work on a small shaft 3?

Yes adapters are avial, usually go for around $400 a pair, they make it so a #6 prop will go on a small shaft III

I can see that putting me back in the same spot beating the snot outta the drives!! Lol

Thanks, what is each drive rated for II, III, IIIa, IV, and V?

Sorry for the hijack.

All good, I was curious about that also

Officially, IIIa's and V's were "rated" for 750 hp, but that was probably the original gear spec. I think the net forged polygon shaft models might have had a higher rating. Most people find them completely reliable at 1000 hp.

III's and IV's are rock solid up to 600 something. People push them much harder, and they last a while, but I have seen gears start to go after extended usage at 850 hp on a SSMIII.

Yes, we make them.