Hi
I actually started with a lime SP for my Mojito and added about 2 cups of the mint infused rum. This last time I actually used lime rum and it turned out really good. That might be a good choice since you are starting with a regular SP. Here's my actual additions...
2 cups mint infused lime rum (I used a good amount of dried mint for the infusion)
1 can of frozen limeade concentrate
Sugar to gravity of 1.010
Cap full of mint extract
Cap full of rum extract
5 drops of green food color
I also add a package of mojito Crystal Light but you can't find that anymore. Another option might be like a mojito cocktail mixer or just leave it out.
Hope this helps or gives you some ideas!