Thank you for getting back to me. We are dealing with a large time zone difference since I live in the central part of the States, but we can work around that.
It sounds like you have a good plan. I have grown raspberries in every type of soil, but they do best in a nice sandy loam. Clay is harder for them to become established and they don't produce as well in it. They usually die if grown in clay that tends to stay wet, and the plants you presently have growing on the site are some that like wet conditions. You'll take care of that with the drainage you plan to install.
When you are ready, it would definitely be best to amend the soil. Bringing in topsoil would be good, but if possible, you can make it even better by amending with some sand and well-rotted manure. If your soil is acidic, you'll also want to mix in some lime.
As for the varieties. If you want an early summer bearer, Malling Jewel and Glen Ample would be good choices. For an autumn fruiting variety, Autumn Bliss would be excellent.
If you have more questions, just let me know. I wish you much success with your project.
My goal is to provide you with excellent 5 star service – if you feel you have gotten anything less, please reply back, I am happy to address follow-up questions. Please remember to rate my service after you have all the information you need. I will greatly appreciate a positive rating as that is the only way I am compensated. Thank you!