Questions about a Freewheel on a Track Frame

use a double fixed hub, can run a freewheel on a fixed but can't run a fixed on a freewheel. hills are fun and easier on fixed. htfu.

I saw a really nice Hubset that was pretty dam cheap, so i thought i'd give Freewheel a try. But i think i will just get a Hub with a double fixed as you mentioned and give Freewheel a try that way.

You would ideally need an Italian threaded freewheel and I must assume the hub was designed for a 5-speed freewheel originally...?

An English / BSC threaded (singlespeed) freewheel will be fine if fitted carefully and with plenty of grease! This includes white industries.
The chainline might not be correct - this can be sorted using spacers to bring it out to where you want or by re-spacing and re-dishing the wheel..
You can use spacers for bottom brackets or order online from velosolo.

I just heard back from the seller who said the Italian thread is a bit tight for British thread Freewheel, and that the Axle has fairly fixed spacing which would be difficult to adjust to single speed without making up some special parts.

This was the Hubset: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=230324349249&ssPageName=STRK:MEWA:IT&ih=013

...only went for £42.23 in the end!