Sonny,
I also spent a fortune on my America. Pretty well everything you could get for the bike, I got. Eventually set it up for single rider too. I replaced the spoked rims with chrome mags because of flat tire issues (can't fix a tube on the side of the road easily). I never increased the displacement but modded the intake to increase airflow, replaced the exhaust with long flow through TORs, increased the main jet size along with the needles on the carbs (ones for the Thunderbird 3 cyl model). I had the ECM modded to hit 8500 rpm from TTP. The bike would break the ton easily. The 790cc engines pulled harder in the higher rpm ranges than the milder tuned 865s which had better mid range torque. The cams for the 790s were highly sought after because of their more aggressive profiles.
Increasing the displacement is easy to do. Kits range from 904cc, 995cc, 1100cc to 1200cc. For those who have the 865cc and don't want to replace the cylinder barrels or sleeve/stroke the engine, there is a high compression kit available complete with cams. Replacing the Mikunis with FCR39s was another change that was needed as engine size was upped. Modded engines could reach close to 105 horsepower. By the time I considered getting into this option, I realized I needed a bigger bike. I was looking at spending thousands on the engine to increase power when for a few bucks more I could have the Rocket. Been smiling ever since.
I do miss my America though. Often ride with the fellow who owns it now. I just might purchase it back from him one day.