I have no advice to offer but a request:
Please do keep us informed of your undertaking as I too have a bicycle and cameras (including the aforementioned Hasselblad) that I want desperately to combine together in a comfortable way. And I am not the only one as I also know two brothers, photographers-cyclists, preparing for some serious touring.
The camera bags I have are not perfect for the bicycle (either on one's back or on a rack) and my experiments in combining the protective material of a camera bag with a regular backpack have been awkward and non practical at best.