Oh my,
KenV 
, my query re. Boeing was intended to establish whether there is some constructional quirk which renders freighter conversion more difficult than it is for other manufacturers' aircraft...
As I already "established", Boeing has made freighter versions of essentially every jet airliner they've built, from the 707 to the 777. The only exception (so far) is the 787 but that's a brand new airplane and a freighter version usually comes decades after the passenger version. There are no "constructional quirks". Indeed there are at least TWO non Boeing companies offering 767 freighter conversions and one offering a 767 tanker conversion. So no, there are no construction "quirks".
Once again, the biggest driver of freighter CONVERSION demand is the availability of donor passenger aircraft with hours left on the clock. If the airlines continue to fly their old passenger jets rather than sell them, there are no passenger jets to convert. So far that's the case with both the 767 and the 777. There are precious few 767s and 777s with hours left on them that the airlines sell off. Although lately, some airlines are converting their passenger 767s to freighters rather than selling them off. It's a simple way for them to break into the freight hauling market.
The A330 is no different. The first A330 freighter conversion is scheduled to deliver in 2016, that's 24 years after the A330's first flight in 1992. 777's first flight was in 1994. Maybe we'll see the first 777 conversion 24 years after first flight, which would put that first conversion in 2018. But again, that depends on the availability of cheap used 777s. And that depends on the willingness of airlines to sell off their passenger 777s at cheap prices. So far, the 777 is holding its residual value very well so that may take quite a bit longer. The operative word there is "may". Once enough A350s and 787-10s enter service, the value of old 777s
may decline. We'll have to wait and see.
As for the 767 supposedly being too narrow to make a good (or flexible) freighter, you may want to ask why FedEX and many other dedicated cargo carriers have bought literally hundreds of them. And these are pricey brand new freighters and not some el cheapo conversion. The A330-200F has the same cross section as the A300/310. So far less than 50 have been sold. So if sales numbers are the criterion (which I doubt), then one would need to conclude that the 767's narrower fuselage is an advantage rather than a detriment to being an efficient freighter.