I must commend you on your boatlifter design. It is sensational (goes with our caravan!) We had it fitted yesterday and it is just so easy, in fact I am sure we will actually get to use the boat more now that we can load and unload without any effort.
We have a Makocraft 3.8m v bottom which has a beam of 1.70m. We use a Custom Boat Loader from Perth [very easy to use and an excellent company to deal with] and I would suggest you contact them as they had no qualms about a 1.70m beam on my LC100.