I'm using 13.5mm spindle wiper arm boxes and a Lucas motor setup , what do you guys recommend for a arm /blade combination ? cheers Jon

Classic mini

look at europa spares and alike you can get adjustable length stainless arms with 5mm or 7mm blade fit in left and right park versions and some 10" or 11" blades

 TEX AUTOMOTIVE, they make custom wiper arms, specific or adjustable length size, different fitting types and even custom crank degrees. Martin and Chris were both very helpful with advice and recommendation, i placed an order on Tuesday morning and by Wednesday afternoon i had the wiper arms and wipers in my hand. Their prices were also very reasonable too.

Take a look on Holden website  This will give you an idea of what you need. Adjustable stainless arms with left or right hand parking angled ends. Also the BMC Mini type blade assemblies and then you know what to go for for from whichever outlet you choose. My screen is 16" and the Lucas motor assembly as supplied has internal cam that worked for me sweep wise. Alternatives cams are available. (Think Snoopy modified his cams himself).

https://www.holden.co.uk/

Classic Mini. From memory one LHD arm and one RHD arm work best.

Thanks for those replies , but I've noticed that my wiper box spindles are 13.5 mm and most of the arms I've seen seem to suit 14.8 mm spindles , I'm guessing the boxes aren't original Lucas ones , any ideas gents?   

13.5 is a LUCAS standard...   

https://www.carbuilder.com/uk/stainless-steel-adjustable-right-park-wiper-arm

Classic Mini. From memory one LHD arm and one RHD arm work best.

Ok , this one's got my interest , why one of each ? 

the drivers lh park sits along the bottom of the screen the passengers rh park sits against the left upright

Mine are both lh park.