should I assume then that the OLD of 130mm is okay for 5/6 speed? Are spacers of any sort required?
If it is a quick release hub measure the length of the hollow axle.
I'm aware of Campag. axles of 126mm. (for 5 speed block, 120mm. between dropouts) and 136mm., which would appear to be for 7-speed block, 130mm. between dropouts?)
There was probably an in-between one- (132mm?) for 6-speed block, 126mm. between dropouts. Perhaps someone can confirm?
I would think the critical thing is to get axle-length reasonably well-matched with distance between dropouts. If you've got that, then messing around with axle-spacers may
be necessary to fine-tune the distance over-lock-nuts.
Freewheel blocks by Regina, Everest, Maillard, Suntour, Shimano- any of these-and others i've forgotten-should screw onto your hub, which is probably an English thread- there will be written information around the shoulder which will tell you. If the hub is English thread, avoid French thread freewheels. (Ask TGR!) IME freewheels go on very easy all the way to the shoulder with a bit of grease. If you encounter any resistance, stop! something is wrong- either dirt or unmatched threads.