The model 51197 (RT55 Tiller) is listed in my old July 1989 BAGMA price guide book..
It is listed under the UK Importers who traded as "Lawnboy", Railway Road, Downham Market, Norfolk, PE38 9EB.
01366 388 540 and 01366 382 041
They still have a website in uk http://www.lawn-boy.co.uk
I know of the brand name but I am not familiar with Lawnboy machinery.
Let us know if you have any joy...
All the best,