Hi Jeanette
I know Birch Hill very well. I passed it every day for 7 years when going to school there

It's about the first steep diagonal road on the
right left off the A5 as you come into Llangollen from Chirk or Froncysyllte. The photo suggests that it might be about half way up.
For a detailed map, you could try the multimap web site.
Some of my friends lived there and I visited. I can't recall the Hollies though.
Birch Hill was still there last July.
I notice that you live in Shropshire. Is it possible for you to get to Llangollen at some point to check.
Gadget
Added
Doh - it's that right brain again - it's the first on the Left not right 