I am installing Holley black pumps for my 502's. Do I have to try to mount them low.... like be gravity fed? I didn't think they did, but now I keep wondering. On all my car stuff, they were all higher than the sump in the rear.... but I didnt know if marine stuff was different???

Nah, just don't mount them too high. Mine's near the battery tray level on a side bulkhead but it's above the tank. It'll be fine as your pump will stop most drain back past it once it's primed anyway. If you have flow problems, look to the tank fittings, that's where the issue will be. My fuel line is 1/2" all the way, but when I looked yesterday I noticed I had a 1/4" outlet and tap on my tank fittting!

Good Luck!

mine are mounted even with the top of the fuel tank, it's been that way for six years, I use a return style regulator and the oil pressure safety switch made by moroso (I think).

Main reason I didn't mount it lower was so I could easily access it. I carry a fully plumbed and wired spare but have never used it.

At the begining of the season I use a jumper on the fuel pump relay to prime the the fuel system. Normally it's not needed.