grams beget ounces, ounces beget pounds.

Building a light airplane is an all encompassing exercise that starts with a critical design review before any wood is even cut (this includes covering selection). A traditional doped silk/silkspan or glassed coverings add considerable strength and rigidity to a structure, which CAN be fed back into structural material selections/sizings allowing for structural weight savings. Plastic coverings add nothing structurally and require stronger internal structure.

I've reworked a few ARF's and put them on diet plans for other people. An ARF diet plan is much harder than a scratch build diet plan because you'll wind up being forced to keep significant chunks of substandard structure and/or poorly selected wood.

In your case, with the gasser brick you've chosen to bolt on up front for an engine, the first place to look is at the engine itself. There's probably several ounces that could be shaved off that gas engine by a machinist (or with a Dremel if you have the patience). Every ounce off the engine is a few ounces less tail weight you need. Putting the engine on a diet plan is a win-win all the way around. Cast cylinder cooling fins and head fins are always good targets for shaving some thickness off. External case webbing can have lightening holes drilled in the corners. Casting flash can be ground off. If it has a steel prop nut/washer, substitute a lighter aluminum hub. Look at any spinner critically. Some of the TruTurns have extremely heavy (like about 4oz) solidish aluminum backplates. They can be riddled with lightening holes and rebalanced to save a couple of ounces.