I think they call for .91 4-stroke so they can claim the 2-lb lighter weight. Say, the kit with 120 Surpass (34 oz) will weigh at least 1 lb. more than the same kit with Saito 100 (20 oz) and lighter prop and spinner.

Perhaps construction has more weight saving measures like wood cut-outs. Even then the weight saving over a GP kit could be at most 1/2 lb. If LG, cowl & pants are made of light weight thinner FB or even CF, maybe another 8 oz. Let's see what turns out.