G'day

I'm with The Parrot. I would go for the smaller engines. Of the three you mention (and I have all of them), the 56 is probably the most sensible but the 62 is almost the same size and weight and so would also be fine. I would not put a 72 in as it is heavier and as I also find that my 72 is not happy working on its side.

I have a Goldberg Cub which is similar to yours. Mine has a Saito 90TS in it. This is the twin cylinder suggested for floats etc. There is also the 60T which is recommended for non float applications. The 90TS does an excellent job of flying the Cub and sounds great too. It is not particularly powerful - about the same as a 62. It has not had a lot of running yet.

I had a previous Goldberg cub which I bought part built. The original builder set it up for an OS Surpass 70 and as I had on I put it in. It had vastly too much power (and weight) and was not nice to fly. So in went an OS 52 surpass and it was much nicer. It even flew well with an old and very tired Enya 46 four stroke. Cubs do not need a lot of engine to fly. They have a lot of wing.