But you'll have a few options. The simplest would be to move the shifter to your left hand side. You'd twist in the opposite direction than you're used to. But I'll bet it's easy to get the hang of that.
Or you could get a thumb shifter from one of the online bike parts houses. Stem shifter? Probably the least useful of the bunch. But it would have one advantage; it would help to cut down on handlebar clutter.
We all suffer this dilemma when converting a shift'r to gas.
I have always just swapped the twist shift'r to the left bar .
As bluegoatwoods has described.
Once you get used to the reverse shifting it works fine....
Should be a good gas bike. It has all of the basic components needed for a successful conversion.... Just make sure not to trust the assembler.
Take it all apart and grease / lube / adjust and refine every aspect of the bike before you take it to 30mph.....
Have a ball man . You'r on the right track......