Both engines have about the same power but the OS 70 Surpass II, While a fine engine, is in a 91 style crankcase and weighs a lot more.

The Saito 72 or Y-S 63 would better choices.

The OS 70 Surpass I is not an engine you would be interested in for your purpose.

You might as well go with the OS 91 Supass II. It weighs the same as the OS 70 Surpass II.

Jim