You can buy the claw from Harris:
http://harriscyclery.net/itemdetails.cfm?ID=963
No need to be welding things. Before you go respacing the frame, are you 100% it's steel? Trying that with an aluminium frame will do bad things, so check with a magnet if you don't know for sure. Why not go for 36 hole? Is it a problem? You could have a 36 rear and a 28 front, perhaps? If you're going to respace, you could do it more carefully using a threaded rod the same diameter as an axle, and some selected nuts/washers inside the dropouts. This will give you a more predictable result than taking a scaffolding pole to it, without costing lots of money or time.