A 120 twostroke will provide more power than your 120 fourstroke and not weigh much more. I might suggest the ASP/Magnum AR 120 XL. I have this engine and it tachs exactly the same as a friends 120 AX (we have both done some mods on them, but still)
If you want to save a few bucks the Magnum is great and if you have alot of $ the AX will make you just as happy. The AX have a muffler that can be mounted inside the cowling for nice clean looks