Hello Charlie,
I presume this is the same Robert Boby company who produced the little single wheeled drill that I know a number of members have in their collections. If so, they were based at Bury St Edmumds. Their drill is very similar to a model produced by Gower, Market Drayton. Boby’s produced quite a range of agricultural related equipment and I suspect they produced your drawings in order to produce those parts for the Rowtrac, ie as a sub-contract fabricator. I believe Bobys had their own casting foundry.–Steve