Maillard large diameter freewheel remover

Actually, the SS freewwheel isn't that much narrower than one of the old 5-6 speed freewheels, which I presume yours is. You'll just have to try it and see how the chain lies. One or two spacers to move the freewheel outward shouldn't pose a problem.

Sounds like I have a plan then! Thanks for the help :)

I've done this a couple of times.
Note there is a difference in converting a freehub and freewheel.
A freehub (cassette - which you don't have) conversion, involves adding spacers either side of the rear sprocket, on the freehub, to determine your chainline, which I would say is easier than what you're going to have to do.

The freewheel type (which you have) I would say is a bit trickier, but totally doable. I taught myself how to do it with the power of the interwebz. I would recommend re-dishing the wheel (which will make it a lot stronger). Then realigning the axle, as it'll be off to one side, to compensate for the 5 gears that used to be on there. You might as well regrease the hub whilst you're there (as it may not have been done for some time.) Then it is a case of measuring your chainline and moving the spacers (washers etc between locknut and cone) from one side of the hub to the other in order to match the chainline at the front. You may need to buy a bunch of extra washers which are fairly thin (1mm, 0.5mm) to swap out for the spacers that are already on there, as they may be 3mm or more, and hard to finetune the chainline with.

I found these incredibly useful - http://www.fixedgeargallery.com/columns/bobgarage/indexb.htm

I'm sure I did a load of other googling when I first did it, but bob's garage was invaluable.

Any questions, then just ask

Good luck, and have fun!

for anyone needing the maillard freewheel removed, Freedom bikes in Brighton has this tool and will knock the thing off while you wait for a few quid.

just incase you search and need to find out who has this elusive thing.