[mr rusty]

enlarger's light output stability???

No. The Enlarger still has it's stabilizer. The step-down transformer just works to convert your power supply as if it was a 120V supply. Depending on which transformer you get you may need to wire up a lead to convert the socket on the transformer to the socket on the analyser. The chain of devices is:-

240v mains => stepdown transformer => 120V mains => 120v analyser => 120v enlarger transformer (with its regulator) => enlarger/fan/bulb

Just one other thought. If you are going to use the analyser safelight output you will need a 120v bulb in the safelight as well.

decent transformer

If it were me I'd get a building site stepdown. Very easy to find, high rating so won't overheat. Even the smallest are probably 1kW. like this:-
http://www.ebay.co.uk/itm/110v-Trans...item43b88819f3

or you could get something like this:-

http://www.amazon.co.uk/Goldsource-S...3617703&sr=8-7

I'd go for 1kW minimum, even though you are only drawing 250-300W.