Robin
Firstly hope you are enjoying your years sabatical, at this rate beginning to wish I had joined you.
Head and 12 valves was all that remained, head had a small mark on one cylinder that could be plannished out, but advice was to reuse especially as it had DVA's expertise on the ports. Rest rebuilt as before forged pistons etc. nothing trick.
I did originally ask for a new engine that was proven to be able to win in class 3, so they said what I needed was an R300 engine.............. Mmmmmmmmm
Best Wishes