Except the temperature in the Esprit engine bay is significantly higher...also, its not just a case of getting a fresh air feed to the intercooler, youve got to get rid of the air that has come through the fins, which will have increased in temperature as it passes..other factors to consider, how big an intercooler would you need to improve upon the existing chargecooler setup, will you be able to supply enough air to it across its full width to make it efficient, if it isnt supplied fully it will loose efficiency drastically...how long will the new inlet track be from turbo to plenum and how will this affect spool up, driving characteristics...
Space is at a premium at the business end of the Esprit so fitting a physically large enough unit with a decent feed and exit for air might be tricky, with some serious modifications required..
The final question would be is it worth it and for what gain...a much larger chargecooler radiator at the front will go a long way to improvements at a small cost and hardly any modifications...not that an intercooler application wouldnt work, it would be interesting to see one done properly..but I suspect it would need to be a dedicated no compromise project...not for the faint hearted!