Thanks for all the help folks.
So, have I got this right? Tillyfar is to the east of Aberchirder. Thanks to Gadget's link, I found Tillyfar.
Tillyfass is to the west and slightly north? I can't find it!!

I've been pootling about with the map since I got in 40 mins ago, and I still can't locate the place!! And I think you're right, Bill. Looking at the OPR, it certainly looks as if it could very well be Tillyfass (what a lovely name!) if only I could find it!

Jill