Thanks for the list of companies supplying Toyota Lexus gear. Will follow them up and see what's available.
Yes the transaxle/gearbox is the weak link, especially since my Esprit has the Citroen box. I am likely to upgrade to the Renault UN1 and get the modification that strengthens it for up to about 500HP. This link describes the upgrade. This upgrade is well known with Lotus and GT40 owners:
http://www.bell-performance.co.uk/gearbox upgrade.htm
It is possible, I am told, to use the Porsche G50 inverted and it fits with some modification. I am probably still keen on the Renault box though for relative ease of fitting and I dont want more than 500HP (not yet anyway). My plan is to take it a stage at a time so I will probably just fit the standard 1UZFE with an adapter plate to the Citroen box as a first stage (risky I know). I know someone in the US running a 300HP Ford V8 Esprit on the Citroen box. Second stage will be to fit a new transaxle and maybe increase the power of the 1UZFE.
Clearly I will need the angle grinder,and a lot of time and patience.
I have also been considering fitting an LS1 or a Ford V8 but the Lexus V8 is still the preferred choice. The length is the big issue but because I will be able to strip off all the extra bits I dont need, like, fan, air, PS etc, I am confident the overall length will be reduced and it will fit in. The Lexus is shorter than the new EFI Rover engines and they can be made to fit, so it should not be too much of a problem.
One problem I am expecting is the fabrication of the engine mounts. I understand police licensing here in WA have new strict rules on this. Anyone know a good Design Engineer I can use for this part?