Info on IPS powered sportfishers

You may want to look at the Salthouse Marine website and check out their 65Q variant that has quad IPS's. In their case it appears that with shifting tanks forward for trim purposes, the need for accommodating the usual gen sets and other gear the amount of extra cabin space created below is fairly limited but nonetheless welcome. There's a comparative weight advantage and less fuel is used by the quad IPS set up so the benefits are not limited to the amount of useable room gained. 4 engines means more servicing costs perhaps but heaps of redundancy if one dies of course. So far the ones built have apparently travelled on their own bottoms with their owners for delivery from NZ to a home in Western Australia so those voyages are several thousand miles including the 1200 mile first leg to cross the 'ditch' (Tasman Sea) to Aussie's East Coast. A confident decision has been made to do this rather than any foolhardy act of faith so I guess Volvo would be quitely pleased that transoceanic reliability is also being demonstrated by reputable people. Good publicity for the design/build quality too naturally enough.

IPS information

Spencer Yachts is using the VOlvo Penta IPS system also. They may have some layouts you can see.

sportfish layout plan in ips powered 56footer

check out the Freedom Boatworks 56. The space savings is impressive-4 staterooms.

What if this drive-leg were turned around such that the props (or single prop) became pulling props as with IPS? And what if this drive-leg housing was incorporated into being the leading edge of the skeg-mounted rudder??

You end up with a truly horizontal prop that doesn't pull your boat's stern under upon hard backing, less drag than a traditional prop shaft and strut, and a big variety of engine placements.

Forgo the extra rotation capabilities of the IPS...and the big extra expense....and control the maneuvering just as you would any twin propped vessel.

(A similar idea is under consideration for a gentleman looking for a fishing charter 55 motorsailer for SE Asia)

You may want to use some caution here, as the patent held by Volvo Penta has extensive verbage about forward facing props being used.
I'm no lawyer, so it may not exclude your plan. Just FYI.