Hello, Murphy - first of all length. 90,000 sounds about right - the average length of a novel is 80,000-120,000 and often a serious historical novel can be longer...it's also becoming more fashionable these days to print slightly 'bigger' books again, so I wouldn't worry too much about your wordcount.
If you buy the Writers and Artists yearbook, or use their online facility, you'll find specific agents who will look at historical fiction - but often you need to read through the whole list beneath each agency to see what individual agents are after.
But don't restrict yourself. If an agent falls in love with your book/voice etc and feels they can sell your book, then they will want to take you on
http://www.writersandartists.co.uk/