Hi Brendan. The 504 would come with a transformer (working) and Timer(not working) So you would need a lens panel and a neg mask of your chosen format. The neg mask (or insert) clips into the carrier which keeps everything central.It will do all formats up to 5x4. Both items can be got on ebay for about 25/30 squids. Odyssey who still make the enlargers, will refurbish the timer, but at a cost. If you know anyone who tinkers with electronics Im sure they could sort it out. Alternatively, Mr Cadd has one sat on his shelf for £95.
I do have a recessed lens panel for a 50mm lens and 35mm neg mask available. I was going to sell them on separately, if your interested.
If you use skype, I might be able to show you it working tonight. Sometime after 9 if I am here.