Raleigh Record Sprint - derailleur question...

[adiwillow]

Hi all, i'm doing up an old raleigh record sprint...

now its been a while since i was last into my cycling, and times have moved on. Basically i need a new derailleur but are unsure of the type i need , ie long cage, short cage, medium cage, 7,8,9 etc.. i have no idea !!

So, what is a suitable replacement derailleur for a RRS ? I dont want anything flash, just a basic shimano or something..

Cheers
adi