Just wondering if there is ANY place/places that has good pre-owned engines for sale? Searching around just inundates you with likely suspect eBay ads. And trying to find ANYTHING "marine" based in Kansas is like trying to find an untouched female on Biden's staff. Or do most people here simply find something salvageable and rebuild it?
I'd like to repower my 252 Islander with a 502 Mag EFI or HP500 EFI.

I'll build you one, pick your poison.............Winter repower 500 EFI's

I was doing the same, searching for a repower and couldn't find any "used" stuff either. Every new build is HUGE power. I just wanted 500 HP so I can keep my Bravo 1. Any more power and I think you'd have to go with a beefier out drive. The swap shop on this forum used to have engines pretty frequently for sale. Just a couple were posted and all seem to have sold.

Just pulled the trigger on a HP 500 I've been contemplating for a while. Literally just sent the deposit 1 hour ago.

I kept going back and looking at these guys. GM Marine & Offshore Racing Engines - boat parts - by dealer -... (craigslist.org)

They are also selling them on Ebay.

The other one I was watching was this. It's not F.I., but it's a good deal. MERCURY RACING 525SC 454CID | eBay

I see them in the OSO classifieds from time to time, a guy just posted a pair of 502 mags with recent long block replacement that looks a bit expensive but is right up your ally. Ad said some drunk driver ran into the boat while parked on trailer so probably a decent set of take outs he might split.

I have a buddy with 2 ea. 509's Willing to split. Built by Known Quality builder and all good parts. He will be reasonable.
PM me for more info and I will get you in touch with him

Yeah...it seemed like there used to be a lot more out there for sale. And for sure I want to stay well within the safe range for a Bravo One. I kick myself in the butt for not jumping on a 502 Mag that was for sale here in the Wichita area last spring for a great price...but at that time I didn't have the 252, just the 208 and I am happy with the 454 power in that boat.
I want to keep this as simple as possible...literally a "take out the 7.4, drop in the other engine and go" type of deal...using same harness, exhaust, etc.

I have a pair of sealed 500 EFI blue motors without exhaust that will be up for sale in the next few weeks. Will run compression before listing. Do not have a scan tool so I don’t know the hours.

I will split them if both are bought at the same time haha.

These are 0 hrs. ready for dyno.

Impressive!!! Thanks for sharing your build thread...

For sale in swap shop, member is in arkansas, posted on 1-25-21, maybe he still has it
7.4 horzion/454 mag