I have been researching and wanting to do the LS swap in a boat for a long time now, and as of this morning, the old SBC 350 has been pulled from my powerquest 230 conquest and the swap has started! The new motor is a fresh 5.3L with an LS9 cam and summit aluminum roller rockers. Im going to leave it fuel injected and hopefully find a way to get o2 sensors mounted in crusader manifolds. I have lots of stuff to figure out yet but the hope is to have it running by memorial day...

Look forward to seeing the progress

Cool project.
230 Conquest is a neat boat.

Should be a fun project! There's a dude on YouTube who LS swapped a formula 242. Not sure if there is anything useful for you but here's the link to the channel

Those are great boats that handle the water great for their size, I grew up with an 89’ 230 conquest. My dad bought it brand new, we got to take the tour of the plant.....not big, but very cool. Good luck on the swap. I hope to see ya out there this year, we are just up the big pond in GH.

Got the motor set in place today so I can start figuring out motor mounts. For some reason I thought the mercruiser flywheel would bolt up but that was not the case, im researching now what the best solution here is going to be. The mercruiser bellhousing did bolt up nicely with the exception of the top bolt on the LS block.

Saw o2 spacers/adapters other dsy on ebay for your exhaust. Lots of $$$$. Like $500 or more.

I know torque convertors need spacer when putting TH350 behind a LS, may be similar with your flywheel issue
I would have thought spacer between manifold and riser would be cheap way to get O2 sensor in there, didn't realize $500
Have seen some home brewed ones if mill and right tap is available

Looks like im going to have to get an LS flywheel and the mercruiser engine coupler will bolt to that. Summit has a flywheel for about $120 that im going to order. I saw those spacers for the o2 sensors on ebay, but im not willing to pay that much for them. Im hoping to get the riser's tapped, or possibly run open loop.

he said putting them in header is that the best place for them ?