I know cost is important to you, but FYI, I have a Saito 300 twin on my GP Pitts (same thing) and it flys it with authority. It balanced perfectly and I use the stock tank. It flys for about 15-18 mins and swings a 20-10 with no problem (no holes any where in the cowl too!!). I have the GP C. Eagle too and will put the same motor in it...I just love the power and sound.