OK... committed, and made a start on converting a perfectly good Magic Pie into something new.... I thought I'd note down what I did in case its of any use to anyone else and I can show my friends what I have been upto!
My second 48v 12AH power source from GM arrived (thanks!). Damn good batteries - done over 1000 miles on my first one and its still as if its brand new...
Here is the new controller, bought from Edward Lynn via the Endless Sphere forum - 18 FET 96-132V 65A - Excellent service from Mr Lynn, and although I only had one Q, very fast response.
Started off by stripping the MP down, I couldn't get the covers off using Bikemad's advice - tapping with a wooden mallet, and if necessary a hairdryer (had a go, but too no avail) and ended up using a large and very sharp wood chisel to gently work off the first cover.
Sans controller, no problems so far.
A bit of solder and heat-shrink (which in retrospect might not have been the best idea as its going to get HOT in there). Hopefully should be OK.
Threading the wires... Ouch, really tight! - used AWG16, bit of ribbon wire, and a very large dollop of Vaseline - ended slicing the last wire into a pencil shaped point to work it in :-)
Once I put the covers back into the MP (thanks to whoever recommended placing a bit of tap on the cover for realigning to bolt holes!) I found I couldn't get the final spring washer on over the wires - resorted to a couple of cable-ties until I find a better alternative.
Lastly, wiring to the new controller. Firstly I reprogrammed the controller via usb to a low amperage so as to not damage anything, then worked through all the control wire combinations to find the correct sequence, which happens to be a different colour configuration to the MP coloured wires (its late and I can't remember the combination, but I will happily post it if anyone wants to know).
So what happened? I couldn't resist having a go at the max setting of the controller - 60amps - and hit 48 mph (on the flat) before chickening out! I am now running at 34amps and do my round trip of 26 miles at 27-33 mph on tarmac and somewhat slower along the towpaths - It will go faster on this setting, but I'm very conscious of peddling and running out of battery steam.
I have constructed a dual battery carrier which holds the batteries on either side of my bike rack - much better centre of gravity as they are quite low. I'll do another post soon with pictures and batteries in series soon.
(Big thank you for all the articles on this forum - answered 90% of my Q's before I even started - especially the user guide -
http://goldenmotor.com/SMF/index.php?topic=1548.0 - which I used for wire gauges.)
Ps. for some reason the images aren't showing in my version of Firefox (mac) hopefully your not all having this problem.