BoatNT,

Fair enough. As a non-industry layman, I can only go by what I hear in passing. So why the bad rep? What are they doing wrong?

Thanks. Brad.

i've been out of the business for a couple years now, but about 15 years ago, we gave them a shot. bought engines from them and we had quite a few issues and just quit using them.
Maybe things have changed now and are better but I don't know

What are you trying to achieve?? You are not going see any performance difference on a stock engine.
UR5's would be fine too. Only slightly warmer than the UR6

Jasper 502 motor
 

I checked all my plugs,wires and cap all look good. Idk when the cap and wires have been replaced. But boat runs fine for a while until it gets warm then it has a misfire around 3500 rpm’s. Any idea what to look into or what to dig into first?

Start with the basics. Plugs, cap and rotor.
The plug wires should be kind of hard to pull off the plugs. If they pull off fairly easily, I'd replace them as well.

after I did those what else should I look at?

1990 baja
 

Trying to replace my belts for a 502 big block serial number 0D336312 and my water pump belt has no numbers on it. Does anyone know what belt sizes I need to look for? If you can provide numbers for all 3 belts that would be great

Take them to auto parts store and have them match the size. Actual Merc belts are 3-5 times the price and no better.