Delahunty drove two or three different Marcos that year, of both Mantis (Ford V8) and LM500 (Rover V8) flavour. The LM500 was shared with Jeff Wyatt, and I think entered by 'Racelab'. The yellow colour of the car in your pic suggests it could also have been the NCK Motorsport car from 1999
Quite a few LM500 entries appeared in British GT over the years, from Team Marcos, NCK Motorsport, and Millennium Motorsport
(
http://www.tateracing.co.uk/images/g,lm500.jpg )
amongst others. No idea how many actual chassis were built- IIRC the Team Marcos cars of 1994/5 were the original factory team which went to Le Mans. AFAIK one of the original Team Marcos cars was run by Skater Motorsport in British GT and Britcar a few years back
http://www.skatermotorsport.co.uk/gallery.htm
http://www.skatermotorsport.co.uk/history.htm