Offshoreonly.com - Holley 4175 (spreadbore) on SBC tuning

I have a 99 Volvo Penta 5.0GL with factory 4 barrel manifold and adapter plate (factory was 2 barrel). I bought a Holley spreadbore 4175 marine carb and am going to install it this week. I bought it from a guy who had a bunch of NOS stuff and I called Holley with carb ##. It has 61 mains and #5 power valve. Anyone have any idea what a baseline would be as far as power valve and main jets? I know VP used this carb on the 5.7GL and I might call holley and get that, if anything that would be slightly too rich. I have tuned some cars in the past (although years ago) but it seems plug readings in the boat are going to be a pain, any tips? Other then too rich is better then too lean. :-)