Having been involved in stage rallies which would now be historic (I started in 73
) but not done any specific historic rallies, other than say Le Jog, which isn't strictly a rally, I'm not sure I can give specific advice, and of course your chosen car is a bit left field in so far as not a mainstream choice.
However, unless you have prior rallying experience, I'd be a little wary of throwing yourself in at the deep end - The Roger Albert in particular is a pretty arduous full-on event, even if not as tough as the RAC rallies of old. I'd look at doing some local rallies to you, maybe even a single venue, even if there isn't a historic class, just to get the hang of how everything works organisationally - even attend a few as a spectator/marshal to get the feel of it.
You haven't mentioned a navigator or service crew - both are pretty essential (the former especially so - says an ex-member of the co-drivers league
) and it may well be worth involving them in any decision process - and of course if they have some prior experience so much the better.
Good luck with it!