RE: Kits or scratch plans?
Based on what I can see of the engine on the Tower web site, I would say that the boat as designed for the .21 engine will be fine for the OS 32. The engine does not look like a power house with the front intake and a pull starter. If you are looking for just a fun boat with no aspirations to race, put the 32 in it. If you some day plan to get involved in racing, the engine is a mongrel. To big for the A Mono class (NAMBA terms) and you'll get your doors blown off in the B Mono category.