stock mercruiser 502 carb, stock fuel pump and fuel system
old plastic tank had some sediment so I removed it and cleaned it.
original and replacement fuel gauge showed 1/4 tank when empty
I assume I need a new sender
1. How do I spec the correct one and since I'm buying a new one is there a recommended unit?
Since the boat is a 99, I believe I should replace the fuel hoses, and I want to add an inline filter
2. Should I order merc replacement or is this an opportunity where I should upgrade?
I have read many things regarding the angle of the fuel tank connections as well as varying opinions on the anti siphon valve.
3. Should I leave original tank fittings on the tank or is this an opportunity to upgrade to avoid future problems?

Thanks in advance for your input

you might just need to adjust the float arm on the existing sender. probably sitting at 1/4 tank part of sender when float is on bottom of tank.

Hard to beat those universal 20$ one size fits all senders for bang for buck .at least pull the anti siphon off the tank and give it a good hosing with carb spray .make sure vent system is correct and enjoy !confirm sender gasket seal is kosher when all said and done so you dont get one of those nasty bildge explosions (its happened to name brand boats with with all uscg approved starters alts ect ect .) I look at every sender seal on every boat now

Consider coal tar-ing the tank before install.

what is the purpose of coal taring?

thanks for the responses from those that did,

Coal tar is a 2 part epoxy that you brush on the tank to prevent corrosion. Think of it as a super thick waterproof paint or tar that dries.

Mark,
He has a plastic tank. I did the same thing on My Donzi tank.
Rust-oleum makes a gallon+quart kit as well.