Horror on the Hill is the only module in the B-series I'm still missing from my collection. They collated a bunch of the B-series modules into a super-module called In Search of Adventure, but the Horror on the Hill segment was edited to exclude the first 19 encounter areas. The fight on the bridges over the lava was always epic. :)
I don't have Castanamir either, now that I'm looking at my checklist...drat!
I just checked eBay for it. Man, looks like I should have held on to those old modules.
It's funny, I remember the toy store in the mall marking them all down to $1 each, marching in and getting everything I could. Then years later when I was moving I took the whole collection to the gaming group at the community college and sold them off for $3 each. I felt like I'd done pretty well.