Hi Peter
A couple of years ago I researched the practicalities of entering the Three Peaks Race. In the process, I looked at the IRC rating and as far as I remember the lifting keel added a small amount to the long winded process but was not going to be a problem.
It turned out that you don't need a full IRC rating for the Three Peaks at there is something called a single event certificate that would cover it.
Martin
335/50