I'm not the biggest fan of coaster brakes TBH so I've not had to deal with a sprocket installation - but from what I've seen it's a simple matter of removing the arm and bending it slightly to clear. Having said that - I would heartily recommend Jim's sprocket adapter
to save you the ongoing headache of sprocket misalignment and the problems associated with it.
I'm not entirely sure why you think it needful to change out your front sprocket & chain tho... Are you referring to the bike's or the engine's sprockets? Are you going for a shiftkit/jackshaft? Or are they just old?
Good ta have ya on the forum in any case, welcome to ya