I've done a bit more on this and constructed a mock-up of the valve gear. It took a bit of working out but so much easier in 3D solid modelling.
I've decided against round rods in the end - that may change when I make them but I am planning to mill the profile on the parent stock, drill holes and use a slitting saw to saw 2 off - might work, have seen similar techniques used before.
All the parts for the engine are now just about done, I just need to make sure i've got all the final versions, carry out the final assembly and start working on the 2D drawings. It's pretty easy but takes some time to get them dimensioned the way I want it and clearly. There are quite a few parts now though, by far the largest project I have taken on so far
I think I might just buy all the metal I need to save routing around for it!
Nick