You can change them over, but it's not the best of things to be doing from a tolerance point of view.
If you are definitely going to do it, make sure that you fit the cams first with a bit of oil on the journals, then make sure you can turn them! If you can't, you need to try another cover, or get the one you've just tried lined bored. Line boring these heads isn't cheap (£500) as they're very labour intensive and also extremely specialised.