Get a piece off an original engine - you don't need much - and take it to your favourite painter to match. Most paint shops will do a free match if you buy their paint.

A clean engine needs only a light etch prime and a spray can of colour for a finish that will last 20+ years...

This - - was done over 20 years ago in Dulux Spraying Enamel mixed to BMC spec (Green Metallic -13261 as I think someone has already said).

BTW the picture (if it shows up:) is quite recent.

Cheers, Ian