front rim size is WM 3.19.
You sure? I would've expected a WM2 originally?
What tire sizes should I be looking for? I am going to be looking at dual sport tires
Originals were 4.00x18 rear and 3.25x19 or 3.50x19(?) front. However, as I posted in this recent thread
, modern-designs tyres with those numbers on the sidewalls are likely to be noticeably wider overall. And you might have difficulty finding modern dual-sport tyres with those numbers.
The overall diameters and widths of Dunlop K70 tyres are online (linked in one of my posts to that thread); even if your bike was fitted originally with Dunlop off-road tyres (Trials Universals?), their dimensions would've been similar. Long story short, you might want to start by looking at the dimensions of modern 90/90x19 and 110/90x19 dual sport tyres, seeing if they'll fit (overall width) and you won't lose too much ground clearance (overall diameter)