Nothing really changes. You set it up virtually the same. Mount your tank on the center line of the carb just as you do with one mounted sideways or upright. Siphoning will not be a problem if you do. This means possibly re-drilling any holes they may have in the firewall for the tank, to move it down farther. Not a big deal, but as noted, very important. If you can't get it down far enough, simply loop the engine fuel line up above the outlet of the tank, and you will not siphon. Draw will be unaffected.

Take your time tuning it, and DON'T get that LA lean. She will be toast in a heart beat if you do.

I'd consider an upgrade when you can, if I were you. In the OS line, Top shelf would be the AX model. An AX55 would run circles around that 65LA. I saw one pull a Top Flight scale Cessna 310 all by itself (about 20lbs) when the guy got the other too lean and it quit. He landed safely on the one engine after a few minutes of flight getting everything sorted out and the gear down. Even a well cared for used one would be a lot better than a new LA. They will outlast any airplane you put them it, over and over. Just as an FYI.