Where on earth did you dig up an SP2P inlet manifold? I spent a lot of time with this manifold back in the day at Edelbrock. We designed that manifold with cross-sectional area runners of two different sizes to broaden the torque curve. The upper plane is the small runners, and the lower plane is the larger. Don't go and port-match the runners because it will just shorten up the length of the small runner. These manifolds were designed to run on 305/350-cid engines and will feed your 265 quite well.
As for mixers, we'd choose one of the later (late '70s, early '80s) 650-cfm Q-jets. They have very small primary bores and venturies. This will work well with the signal from your baby Mouse. If you can keep your foot out of it, you should see the best mileage from the Q-jet combination.
Building compression is always tough in small-displacement engines. Once you have unshrouded your valves by opening up the chambers, clip the heads to get the chambers back down. We'd shoot for 9:1, or more if you can. Increasing the compression is going to be free mileage, and you would be safe up to 9.5:1.
Hope these tips give you some ideas for your Mouse. Make sure you go out and stretch its legs every once in a while. You will be surprised how well this engine is going to run. Good luck and happy cruising.
Technical questions for Kevin McClelland can be sent to him at firstname.lastname@example.org.