Most older lights should be able to be retrofitted by cutting down the brass contact on the back of the head, to allow for a longer battery chamber. Those contacts are too long anyway, there's no need for it to be anything more than a thin disc of metal. I've cut down the brass contacts on all the peak lights I've ever owned, with no ill effect whatsoever.
In other news, if the new pill becomes available for the CR123 bodies, I want one. I have a McKinley head on a QTC body, and the QTC is already getting jumpy.