Actually it could well be down to the size of the pits. It's possible the pits are about 11 metres long, so could cope with the likes of the Leyland Lynx, and various high floor single deckers, as back then they didn't have to build to the full 12 metre length to make up for the lost of seats which modern low floor vehicles suffer from due to front wheel arch intrusion and provision of wheelchair and buggy bays. Plus the last of the high floor single deckers Hartlepool had were the Volvo B10M which are mid engined vehicles with the engine in the middle of the bus.