[spareparts]

I have never seen one of these set ups personally, but assuming it is the GM 250 cu inch I-6, you can use a number of aftermarket manifolds rather than go back with Volvo, you may have to modify the exhaust a bit to make it work, and maybe some cooling mods too, but it shouldn't be too bad. If the carbs start giving you trouble, you could change to the mercruiser 165 set up with a single 2bbl rochester. Or even use the mercruiser manifold without the carb adapter plate and bolt a Q-jet on it like they did on the 292(200 hp) Mercuisers. Putting an I-4 in there might not give you the torque you're after. The drive itself should hold up under most power options. If there is room in the boat, a v6/8 could be a swap option, keeep an eye out for a ragged out late 70's, early 80's bayliner(they used Volvo drives) that has a good engine/drive for a complete swap out, they can be found cheap. All the aquamatic drives had the same hole in the transom. Changing over to a merc or latemodel Volvo would require redoing the transom