10.000 Pounds ???!!!??? (that is around 14.000 EUR !) I can't believe it! Take a look at www.mobile.de (a german add site for all kinds of cars), one can buy a 1988 BMW 750iA for as little as 1000EUR (that's approx. 1150$). Here is the link for a quick look: http://www.mobile.de/SIDkNYcierRHSbIGzr-zFos4A-t-vaNexlCsAsK%F3P%F3R~BmSB10LsearchPublicJ1059938248A1LsearchPublicCCarY-t-vctpLtt~BmPA1A1B20C639e-t-vMkMoSm_xsO~BSRA5D3500C750C750A0A0/cgi-bin/da.pl?bereich=pkw&id=11111111123179912&top=17&
In my opinion, you could (theoretically) make a trip to germany and buy a well maintained one for EUR 2000 - 3000 and then load it onto a ship and send it home (that isn that expensive as well) - it would cost you in worst case no more than 7-8.000 EUR (I'm not certain about the import taxes however), which is half the price people want for a 750i in your country. All that of course if you can speak german (Germany is homeland of BMW, so the high number of BMWs there makes them quite cheap (rules of market:)) and one surely must be a bit of adventurer to take on one like this... but still it's possible.
Regarding the tranny - the best option is a porsche of course, but those are really expensive (even here in Europe one must pay at least 2000-3000 EUR just for the tranny and that's of course if you can even find one). Since we're dealing with engines capable of around 300HP (284 for the Jag and 299 for the BMW if I'm not mistaken) the Renault UN1 transmission should do just fine as well. These transmissions can be found in the following Renault models:
Renault 25 2.2 ltr 4 cylinder; The 21 Turbo; Some V6 injection Renaults and all the V6 Turbos.
If you can't find any of these options I would recommend contacting a company specielized in building (mid-engined) cars, like the Parallel Designs (http://www.paralleldesigns.co.uk) for instance. That kind of company can inform you about various drivetrain options, and finally you could simply buy an engine with the clutch and tranny already attached to it from them.
