So I came across a thread on one of the Telecaster forums talking about a Surfy Bear kit. Turns out that this thing is a clone of a genuine vintage standalone Fender reverb unit but using JFets (transistors) rather than Valves but following exactly the same circuit as the original.
Came in kit form from a company in Scandinavia with a fully built PCB, with pots and wires and other bits - provide your own spring reverb tank power supply and case etc . Me being me and having lots of bits sitting around, including several spring reverbs from Hammond organs, I immediately sent off for it and it arrived in a couple of days.
Meanwhile I was looking around for something to put it in and being too mean to spend £300 on a clone of the original fender case, I picked up a broken Fender practice amp with a little 8" speaker on Ebay for £7. Scrapped the broken amp PCB and speaker and but kept the chassis and case and spent a day in the workshop chopping it down to a mini head size and managed to shoehorn the reverb spring into it with a bit of judicious chiseling. Added some Fender grill cloth to give it the right feel and for fifty quid ended up with a very nice dinky little unit that not only sounds the part but also looks the part.
And it worked first time :)