If you have the correct tensioner and crankshaft sprocket fitted then the next common cause is deformation of the back plate due to being overtightened to the block or the pump bracket pulling the pump out of line.
It may be worth replacing both if yours keeps eating belts.
I think you're right, the housing has to be bent (there's mention of this in several places on the web)
Looking at it logically, all pulleys except the IP pulley are either bolted to, or run in bearings in, the cylinder block. So the most likely candidate for being out of line is the IP pulley which sits on a comparatively tinny lump of alli.
I've fitted a "one piece" crank pulley and I' m hoping that with the flange intact, belt wear will be minimal and that it will stay in place. I'd surmise on the old pulleys constant pressure on the spot welded flange broke it off and once the belt could rub on the cover, deterioration was quick.
I'll see what happens to the belt over the next few months and if it looks like it's starting to wear (if I make a special tool I can measure the belt in-situ), I'll try and pick up a second-hand housing and check out the possibilities of skimming it square again. That will obviously effect the cam and drive belt alignment but it may be doable.
