Dear phillip-s
This is going to be your lucky day! And a free ident from The Hall & Duck Trust
Your Ransomes MK 10 No B3413 is a 20 inch machine, You are correct to say the mark started before WW2,infact the first Mk 10’s came into production at the start of 1936.All Ransomes motor mowers had suspended production in 1940 except for Gang Mowers for airfields, After the war the Mk 10’s were still in production from 1946 -1947 with pre war parts, there after 1947 – the end of 1949, with new parts.
Your machine from Ransomes records which we hold states B3413 was made in February 1947,so using pre-war parts.
Your engine is a 248cc RSJ (Ransomes Simms & Jefferies) which is centrifugal
Hope this helps you