Have you considered a Lotus manifold? There are stainless ones made for a lot of the engines. You'll find
https://www.thelotusforums.com/ a mine of information and Bibs the guy in charge is an excellent friendly and knowledgeable guy to know.
http://www.lotusbits.com/ is a good source of parts for older Lotus
http://www.deroure.com is the site to go to for parts still serviced by the factory
The latter is part of Bell & Colvill, the world's oldest Lotus dealership. I'm the IT manager there