Spread Thin Across the Toast of Time

I'm writing two books at the moment. One is set in Cambridge in the 1890s but deals with Egyptian antiquities from (very roughly) 2000 BC. The other is set in Orkney, round about 2500 BC, but includes a character from 2500 AD ...

It is quite possible my head may explode.

How I find myself in this position is a long story I won't bore you with. Of more interest is whether or not it's possible. I've never tried to write two novels simultaneously before, and certainly not two with such disparate time frames. Will I find myself putting 26th century tech into the hands of my Victorian detective? Will my Stone Age heroine start speaking in cockney rhyming slang? Will the two books merge imperceptibly into one gigantic surreal entity, leap out of the temporal toaster and go rampaging off across the kitchen of eternity, thereby making it difficult for me to meet my deadlines?

Stay tuned and I'll let you know how it goes. For now, I think a break is in order - I find myself strangely peckish ...