Okay, for everyone who's been following this thread, I've just had a brainwave. I'm now thinking about using a chord section of a fairly large sphere e.g. 4" - 6" (cutting a "dish" section out of it) and using that as the "shroud" part that will cover all the internals.
Go to
www.mcmaster.com (tons of really cool stuff... we use them a lot at work
) and search part# 3748K19... it's a hollow 6" polypropylene ball. PP is easy to work with and paintable, and it's cheap too! I got thinking earlier today that since the shroud will be covering most of what was the original headlight reflector, I can cut most of that reflector away and free up lots of room for the internals.
Thanks 06Fg2 for the RX330 pic... that led me to my idea. I'll do a few more measurements, decide on a good diameter and if any other materials are available and order a few. If I do this, I'll have to revise some of my ideas on the mechanical bits.
Stay tuned