There are several options. The easiest being that you aquire a range of pedaling gears to assist in climbing tough hills. This requires NO modifications to the drivetrain OR engine. If you have a single speed beach cruiser, you can either buy a wheel with an internally geared hub or upgrade to a mountain bike. If you don't want to pedal at all, you can add a shift kit. You can also use a large displacement 4 stroke, but this will be the most expensive option because you will need a drivetrain that fits, and there are only two commercially available. If you are in decent shape, you should be able to pedal assist up those hills no problem. But it's up to you either way.