I've just spoken with jenvey dynamics in the link above

I've been working with them for many years now

They can do a package which includes throttle body from 45 to 55mm, spigot adapter to attach to a custom inlet manifold and the another spigot for a filter to slip on to, they will build it all up and machine them all together so that there is a nice smooth tapered bore. I have found 9 degrees to be the optimum.

There sales guy Simon is getting me a price later today

I've been a dealer for jenvey for many years now do can get good discounts if anyone is interested in going this route