I currently have auto meter pro comp marine gauges that were installed by the previous owner. I'm finding that a lot of the original sending units aren't allowing the gauges to read correct, like fuel, oil pressure and water temp. Plus the 2 sets are in different increments, like the port motor reads 20 40 60 80 on oil and the starboard reads 15 25 50 75, sa,e with volts and water temp, real annoying.

So what gauges can I buy that will work with original sending units? It a 1988 454/425's Formula 311 SR1.

Thanks for any help.

It really depends. Even different gauges from the same company might need different senders.
You need to know what you have and then go from there.