As per Martin's comment above, the Kendal members can almost certainly help.
But - a very useful source of information is the KCC 50 years journal (2007). This is actually dedicated to Dave Heap and contains a lot of information about him - in it he's described as the "architect of the club".
I knew Dave reasonably well myself. He was a was a heavy smoker and, tragically, he passed away at the age of only 53, from cancer. (I can't confirm the date but it was at least as long ago as the mid 1990s.)
The two things he's perhaps most remembered for are his classic Dales caving book "Potholing Beneath the Northern Pennines" (which, along with Gemmell and Myers' "Underground Adventure" inspired me so much in my early caving days) and the huge amount of energy he put into encouraging youngsters into caving, over a great many years.
I don't think Dave wrote any other caving books but I think you'll find he contributed good quality written material to the several KCC journals and Newsletters.
The journal mentioned above is a very fine publication in its own right anyway but anyone wanting to research Dave Heap's contribution to northern caving should probably buy it.
(If you want to do this, send me a PM and I can put you in touch with someone who can sort you out. I'm not a KCC member by the way, so my recommendation is genuine.)