Thanks Wojtek and David.
I've now got the exhausts made and fitted, as well as the fuel inlet pipes and the ignition wires. Once they've all fully set, the area will be cleaned up and any gaps in the joints of the pipes sealed, before painting. The engine cylinders will also be re-touched, and then the collector ring fitted, along with its support rods, the latter made from stretched sprue.
PICS 1 and 2 show the pipes, made from plastic rod, and the inlets and ignition wires, made from stretched sprue.
PICS 3 and 4 Show the exhaust collector ring / cowling temporarily fitted, in order to check that the chamfered ends of the pipes match up with the internal ring. As with the port collector ring, the manifold outlet has been drilled out and filed to an oval hole, and the breather pipes added, again using plastic rod with the ends drilled out.
There's a few more small jobs to complete, including sanding off the unwanted parts of the framework on the early-style canopy and polishing it, before this is fitted, and then the relevant parts of the model will be masked, ready for the initial paintwork.
Thanks again for your interest and comments.