10mm Reamer and 10mm slotmill arrived today. Tried the slotmill and this give a slightly oversize hole. Reamed hole was a lot better. So pilot drilled all way through at 3mm, followed by 9.7mm and then 9.9mm, both these stopping 2mm before the bottom of the plate. Then ran reamer through all 56 holes.
The dowels just need a firm twist to insert them. Will make a small threaded tool to remove them.
Pleased how it came out.
Will try on the mill tomorrow with the indexer.
Thanks for all the help and advice.
Colin