What has worked well for me (496 B) is an older MP high volume pump slightly overdriven (6.25" crank pulley, ~5.75 WP pulley). Cools great including AC. Bouchillon has a good selection of pulleys. That's where I got mine. The MP pump is no longer sold. The Milodon may be OK with correct drive and Mancini sells their own brand high volume pump as well.

I'd start with the pulley.