How can you tell if an old frame was originally built to take 27 inch wheels or 700s?

Are all 27" wheels the same? If I bought a bike with 27" wheels off eBay, could I pull the wheels off and use them for a Raleigh Misty? Could use an expert opinion. Also, anyone in London fancy helping me get Misty back on the road? I am utterly clueless about bikes and just want to get her on the road for the least money. If I got a lesson in bike mechanics too that would be awesome.

I've built a Misty. The spacing on the rear is 120mm and they were built with 27" wheels. So I imagine you could probably pull the wheels off the Ebay bike and put them on the Misty, yes. I doubt a bike with 27" wheels would have 130mm spacing. Not all 27" wheels are the same - the rims may be slightly different widths and they can be made of steel or alloy - but they should fit a Misty.