Classic & Vintage - campagnolo freewheel

I've inherited my dad's 70's merckx with a full campy group. I think I may need a new 6 speed freewheel for it, but I've got no idea where to look for it. i've searched the internet but I can't really tell which freewheels are good quality (I want it to be the same quality as the rest of the components) and I can't find any that are closely spaced (for triathlons and such).

tim
(as you can tell, I'm not a gearhead. I ride a fixe and haven't ever had a bike with multiple gears in my life. so please excuse my ignorance.)

www.harriscyclery.com has a few offerings under "freewheels" that would probably
fit. Big question will be does the rear hub have "English" or "Italian" threads. Maybe
your father knows. Merckx bikes have been made by a wide variety of manufacturers, large and small over the years. The Harris freewheels are probably
all English threaded. www.sheldonbrown.com should have a discussion of threadings
for various parts of the bike that may give you a clue as to which you might have.
IIRC the Campy BB threaded parts should be stamped with their thread size, if this
is the Italian BB thread it would suggest the wheel is also, and ditto for English threading. Steve

If your rear dropouts are spaced 126-128mm instead of 120mm, you can upgrade to a 7-speed freewheel, such as an SRAM or a Regina. These are relatively common on eBay.

http://www.loosescrews.com/ has five and six speed freewheels that can be custom built to whatever spec you need. They are Shimano. As John E said, if the dropouts are spaced 126mm, you can upgrade to a 7 speed freewheel or cassette.

I checked my old Campy BB cups and they are indeed stamped with the thread size on both sides.
The BB thread size should be easy to read on the L side and if labeled 1.370" x 24 TPI it is
English threaded, and by inference the wheels are probably English as well. Steve