I understand what you are trying to do.
A change to 26:27 would give you less gear than your current Adventure 6th?
The major reason why I took the Super Duke gearing out was that its 1st is higher and 6th lower than the Adventure gearbox. If I sprocketed for low speed stuff, the higher speed cruise was compromised and visa versa.
Your Adventure gearing is currently the widest spread of gearing on any of the LC8 engines. In other words you'll not get a lower low or a higher highest gear in any other model LC8 Engine unless you get custom made gears made$$$$.
You seem to be looking to gearing to solve a consumption issue. Sadly these engines are not known for their efficiency so do what I did....
Get bigger tanks!