6 or 7sp freewheel with 9 or 10sp derailleur?

Thanks for the replies everyone.

I've got 10 speed Ultegra F+R mech with a 7 speed block and chain. Works a treat - really nice shifting

Really? Thats interesting to know. You managed to limit the side to side movement with the limiting screws no problem? What shifters are you using? Indexed?

Why not using a nice XT long cage derailleur with XT thumbies and the correct chain?? Would maybe fit nicer to the "older" bike... or whats with Suntour Winner Pro freewheel up to 34 combined with some nice older Suntour equipment? They made nice parts in the 80es..

The newest XT you mean? I was looking at the XT thumbies already. Those look like just the job.
The bike currently has an old long cage Shimano "Stags head" 600 derailleur, but it won´t handle 34t and I don´t know if it´ll play ball with indexed shifters. My other plan was to use a Stronglight 49 chainset with the old TA cyclotouriste rings and go way down in size on the front, instead of bigger on the back, but again, I need a derailleur that will handle that amount of difference. Not sure if my current one would.