First, I was wrong about the oil, it should be SAE20 not 30. In the day it would have been Castrolite or another manufacturer’s equivalent.
I knew that I had a very good guide to all things Wico series A tucked away somewhere and I’ve just unearthed it.
http://www.wizardclassics.co.uk/douglas
Maintenance Manual for the Wico Series A.
Edited by and additional content by Peter Chadbund
I’ve got another useful booklet which is a reprint of a Wico publication. Reprinted by David W Edgington, Lodge Wood Farm, Hawkeridge, Westbury, Wiltshire.