I discovered that Meng make nuts and bolts for scratchbuilding, I only wish I had found this out earlier, the grey ones are Meng the tan coloured ones are my own heat formed items.
Here is the finished compressor head with Meng nuts and bolts added.
In my hand to give some idea of the size.
I added some copper wire for the pressure hoses that run to the cylinder heads.
Looking into the engine compartment.