You're quite right Harry although there's a vehicular entrance straight into St. K's about 100 yards down the road from the entrance to the West Nec.
I've been playing with maps again, and have marked both vehicular entrances with blue dots, and the original entrance to Lambhill with a red X.
The simplest way (I've found) is to turn off Balmore Road at the traffic lights into Skirsa Street, then take either the second or third turning to the right which both lead onto Tresta Road. The entrance to St. Kentigern's is exactly opposite the top of Fara Street (which you can't see because of the red letters!) and the Western Necropolis/Crematorium is just along the road.
wn = Western Necropolis, sk = St. Kentigern's
Anne