Mercruiser used a mix of Ford (virtually only 302s for the Ford mills) and GM till the early '80s, then all GM after that.
My family has a 1991 Chris Craft boat with an OMC Cobra 351/5.8 engine, which produces 235 horses in this form. It uses a largish Holley carb and is totally stock, and still runs well. It is a 21 foot boat and I can just kiss 55 mph.
OMC used a mix of GM and Ford as well, as did Volvo. Volvo sterdrives bought up the OMC Cobra line, and they had at least a few models of 351W engines through about 1997 or so, maybe a year or 2 earlier. Some were fairly hot GT40 fuel injected models, though they're rare.
OMC also used Ford's 2.3 and 460 V8 engines in the late 80's and very early '90s. The 460 was sold as both carburated and injected, though the injected 460 King Cobras are VERY rare, and it is next to impossible to find stock replacement exhaust manifolds for them.
Another Ford engine was the weirdo 3.7 liter Mercruiser 470 sterndrive. It was half a 460 with 1 460 head on it (I don't recall which.) They are widely reported to be absolute junk, but it was at least a decent idea for an economy motor.
The 351W was very popular for inboard direct drive, tournament ski boat installations in the '80s and '90s. Pleasurecraft Marine and Indmar (at a minimum) both had various versions of this engine in carburated and injected form and the 351 was seen as "the" towboat engine for professional water skiing boats such as Mastercraft, Correct Craft (Ski Nautique), Supra, Ski Centurion, and a couple dozen other manufacturers. Mercruiser sold inboard engines during this time, but they weren't competitive until the late '90s at which point they and Indmar ruled, all with GM iron. The 351 was preferred as much for tradition as it was for marginally better torque than a Chevy-based Mercruiser 350.
I would also point out that the 3.0 4 cylinder engine used to this day by both Mercruiser and Volvo is a Chevy, and not the Pontiac "Iron Duke." This engine has its roots all the way back to 1961 or '62, when it was the 151. This engine has got to be one of the longest-running designs out there.
In the early 1990's, my family had a large direct-drive inboard ski boat, a Supra. This boat was 21+ feet at a time when most boats of its type were around 19', and though the 351 marinized by PCM was the standard engine, ours had a carbed 330 hp PCM 454. We always thought the 351's sounded "tinny." It drank ridiculous amounts of expensive marina gas, but I could pull my 300+ pound dad up on a slalom ski with about 1/3 to 1/2 throttle with 6 or 8 people in the boat.
Chrysler also had a large presence in marine engines, though they were basically finished in 1980 or so. They did have their own sterndrive line, but nobody bought them, and instead they did a lot of V-drives and straight inboard stuff. A friend has a Century Cardel with a Chrysler 440 V-drive, and I'm here to tell you, that boat is one baaaaad mf-er, on top of being gorgeous.