Rob: I use a big oven roaster (turkey size) pan with doors cut in the ends. I put water in and sit it on top of a single element hot plate. I've used this to straighten bow staves and the key is definitely to get the wood to the right temperature through and through. When it's correct the wood bends like plastic- quite amazing. If you get it wrong it cracks. For rifle stocks I prefer the boiling linseed oil/ torch method as it doesn't seem to affect the wood at all. The secret, as with steam, is to get enough heat in. I've had good luck with a few and had others crack. My best result was with the forend off of a '41 Fazakerley which had a nasty bend and twist. Straightened it with hot oil 4 years ago and it remains straight today. Regarding the gun in this thread, with the collector value of a good Mk I, I don't think I'd touch it. If I was intent on shooting it a bit I think I'd just try it as is or, better yet, shoot a different one.
Ridolpho