I just sold my Valkyrie. When I bought it it had been sitting for over a year. I had to pull the carb floatbowls and clean the out, lots of sediment.
I would recommend that you pull the carbs off and rebuild them completely.
Also, take the tank off and thoroughly clean it and flush the fuel lines.
The issue with those flat engines is that if there is trash in the fuel system, and it gets in a needle valve and allows it to flood a cylinder, the gas will lock the engine up when you try to start it. This can cause a bunch of trouble, broken starter drive or rear case (don't ask me how I know

), or even a bent rod.
After you have totally cleaned the fuel system, I would start it up and let it run a little, watching for anything that doesn't look right. I did this several times, then took the bike for a short ride. Then changed the oil, and coolant.