What is a good fuel pump for a genv that runs off of the water pump. I was looking to replace the original merc pump with a holley or something similar.

That is not the same mechanical pump as a standard Chevy pump. The arm on that pump is different than a standard pump, so you have to use a Merc. style pump. However, you can replace just the lower pump section of your existing pump. CP Performance has a real nice pump section.

http://www.cpperformance.com/p-12460...6-engines.aspx

Hope this helps.
Eddie

Thank you that was what I was wanting to know.

Glad I could help.
Eddie

While on the fuel pump issue, what would you suggest for a 2000 500EFI with an electric pump only? Stay with Merc or go aftermarket?

I would stick with the electric Merc pump in your case. It will be much easier and cheaper in the long run to stay with the stocker. If you go aftermarket, then you will need to redo quite a bit of plumbing to make it work.
Eddie

I have been running one of those for four seasons now, It is a good pump to upgrade to.