any one have any sugestions on a good mechanical replacement pump

I run a block mounted Holley 110gph. Works great.

sea pump mounted ??

Yes sea pump mounted gegs and summit list a holley marine pump but not sure if block or sea pump mounted

There's only two. Do a search here for the part #'s.

One is from Airtex (who made it for Merc) and is cheap $$$, and the other is a big dollar unit from CV Products.

Okay, here is the Airtex:
Airtex 60932 Mechanical Fuel Pump for 1992-93 Mercruiser Marine 454 and 502 8 Cylinder
by Airtex
Link: http://a.co/j804khm

And I was wrong, there is another choice. F-2Speedy posted this in another thread. Made by Carter:
http://www.ebay.com/itm/CHEVY-MERCRU...mtr&rmvSB=true

And they seem to be good pumps, although I've only ran them on engine stands,