My CB750 K2 is U.S. Spec. and insured with Footman James on a multi - bike policy (VJMC Scheme). This has not posed any problems. I also checked this year that they had recorded it as an import whilst I was reviewing other information with them (my request, as I have been with them for some 15 years I do this from time to time) and they had it listed correctly. They did, as a matter of interest say that the premium is unaffected by this.
In the past I used other brokers and insurers and might do so again in future, however I always came across problems at some point - usually when insuring my one "new" bike that I use for touring, alongside the classics. Under my policy, I am able to run as many classics as I want (for an add - on fee) however, there must never be more modern bikes than classics on the policy. It also includes the usual European and UK breakdown cover as well as other common insurances and allows me to ride other classics (must be over 20 years old) on third - party only cover.