My advise would be to do it yourself if you have the room.
Their are very few people I would trust to work on my vehicles, not only that but it gives great satisfaction when finished and driving it. And they're good fun to do too
Got my chassis from Richards and very pleased with it.
There is a guy next door to them that does the chassis swap if you don't fancy doing it yourself. Give Richards a call and they will point you in the right direction.
Better still, do it yourself and save some cash, it's not a difficult job to be honest.