The reason that you cannot do a "bleeds off" on the (GE CF6) 767 is because the ADP is on the centre hydraulic system. If you attempt a "bleeds off", the ADP will not run sufficiently on APU air only. I've no knowledge of the PW version though.
Gear and flap retraction is very slow, shortly followed by "gear disagree" and "flap disagree" EICAS cautions.
Colleague of mine found this out after an engineering request.