7/70 on thé id plate. Seems a lot were pushed out that month

Your right Jr - ira been mucked around with - at only 1632 km?! Dee what else i find

The engine internals would tell a story. Condition of valve guides and seats, bores would show cross hatch with no ring mark at top of bore, standard rings and pistons with no wear, and lower down original bearings and crank with no wear, and original asbestos clutch plate with virtualy no wear. 

just Googled Dunlop Sp41 tyres.....
Longstonetyres says   (http://www.longstonetyres.co.uk/page/dunlop-sp41)
The Dunlop SP41 was Dunlops first commercial venture into marketing the new radial tyre technology. The SP41 was sold alongside the C41 crossply tyre from i believe 1963 until 1968. In 1968 the Dunlop SP Sport tyre became the most prominent radial tyre from Dunlop. I'm afraid i cannot confirm these dates exactly but from these period fitment guides it appears that the SP Sport takes over in 1968.
So if you have 5 tyres the same, with little wear then looks like original miles. The tyres may also have a manufacture date moulding, like the modern DOT number.
 
Plug leads were probably 1/4 inch (i.e. 6mm), like a 1975 (other brand) thing I have in the garage. Leads have become thicker over the years.
 
This is not a barn find, it's a time capsule.