Looking for more go!

Currently: Burton Big Bore 650cc, Power tube, Ecas/Bourbor two in to one straight through exhaust and bigger bore silencer. Gammatronix points assist.

Considering fitting an AMR 500 Supercharger or do I go all out for a BMW conversion?

What worries me with the BMW is:

if the insurance went sky high.

Brake Cooling Ducts, I believe to be important but seem absent on the conversions I've seen.

Sorting out the Heater.

Too much power? Ive heard of clutch plates rivets snapping and other drive chain problems.

How far does it stick out of the bottom of the chassis? I have heard of ground clearance problems.

And most importantly which would be the most fun?

Nice set of options.
Moto-Guzzi V twins are a much better fit in a 2cv.

Sombody local drives a Moto Guzzi engined lomax and it has a really nice sound.

What about getting re-test and registration? Do I need the paperwork to go with the donor bike engine for UK test?

I don't think an engine swap, is regarded as a "Radical Alteration".
Search on this forum http://www.citroenspecialsclub.org/forum/
MOT is based on the vehicle age?
Insurance is the main issue (in these times of ligation), if you follow me.
My 2cv 4x4 costs £154 with FJ because it is modified:(

I don't think £154 fully comp, with agreed value and unlimited mileage, is excessive. Especially when you add all the other benefits too, like UK & European breakdown cover. It'll cost you more than the premium for 2 weeks cover through the AA or RAC. I'm insured through FJ and it costs me about the same as you, but a standard car. Though I added the Morris Minor to the same policy for an extra fifty quid, and that included a £25 admin fee. Bargain of the century.

Go for AMR 300.
Thinking of doing it my self.

how about a gs 1.3 engine with a visa bell hosing ?
fits superb ive heard and engine upgrade like bigger valves and opening and maybe one or two smart turbos or a compreser maybe

Citroen GS, GS/A engine is so 1980s.

Seriously though, they leak oil like the Exxon Valdez and aren't as good an engine as many out there that can be used.

I'm paying arround £120 at the momoment with 2 named drivers on 650 modified as long as it doesn't go £ 300 + I'd be ok for the BMW.
Where can you get a visa bellhousing these days it's all of it suddenly become as rare as hens teeth!
I suddenly have the chance of a BMW engine, do I need paperwork to go with it?
I don't want find out its not road leagle!

Looking on the UK DVLA website for a "Change of engine number or cylinder capacity" you need to provide EITHER :

A receipt for the replacement engine
Written evidence from the manufacturer
An inspection report provided for insurance purposes
Written conformation from a garage (if the conversion took place before you bought it)

So, if I have understood this, all I need is a receipt from the seller.

Paperwork here in the UK hopefully should not be too much bother!