Pump gas compression

Honestly - you can ignore the static ratio. IMO the first step after you know the stroke, rod, piston, and head package is the camshaft. After that comes the static ratio and that's only worked out after the dynamic compression is figured out.
I have 91 or 93 octane w/10% ethanol in the ground here so my self imposed guidelines: W/aluminum head, closed chamber, built with quench tighter than .035 - I use 8.75:1 as my max dynamic. You could do something with less dynamic if you want a cushion. Less dynamic can be from a larger cam or a reduced static ratio.
IMO you are much better served by using a mild dished piston rather than a flat top and milling the heads to reach the chamber size that makes it work. I ran a few numbers and a static somewhere just over 11:1 will give a dynamic around 8.-8.5:1 depending on the camshaft. I was using an intake closing event of around 70° ABDC.
Also IMO - if you're going with the 4.25 stroke and that top end I'd be looking for something in the 265-270° @ .050, lift in the .600-.650 area for it.