To narrow it down to seven riders is almost impossible, IMO. By far the best I've seen has to be Ove Fundin, head and shoulders above anyone else. The rest, well FWIW.
1. Ove Fundin
2. Ronnie Moore
3. Ivan Mauger
4. Barry Briggs
5. Peter Craven
6. Sverre Harrfeldt
7. Split Waterman
The last one ought to create some discussion!
As for the almost made it list.
Gote Nordin
Peter Collins
John Louis
Ole Olsen
Ole Nygren
Gote Nordin
Ken McKinlay
Nigel Boocock
Bob Andrews