ANDREW - Actually HOT Roll sheet should be good enough for a blade, I hope Your design includes some reinforcments like angle iron, round tubing, etc. along the lengths of the blade close to the scraping edge and top of the blade. Cold Rolled sheet which is just a bit stronger but has a much smoother finish gets much more expensive. I'm not real familiar with the OEM IH CC blades but I suspect they're made from steel less than 1/8" thk. The 80" wide blade I use on My 30 hp Super H ia only 1/4" or 5/16" thk. Check the website for Sno-Way International for ideas how they make the reinforcements for their blades. They make pickup truck snow blades with clear Lexan moldboards. All the strength is in the frames.
Art & I are biased towards Blue welders. But between a Craftsman and Lincoln I would definitely go with the Lincoln. Before You buy a little gas-less MIG I would check Your local Craigslist and see if someone has a bigger welder for sale, Lincoln, Miller, ESAB, Clarke, Century, Hobart, even LINDE have made production MIG welders. Craftsman buys their welders from Lincoln if I remember right. Gasless wire welders are O-K but You lose the benefits of MIG without the shielding gas, lots of splatter & slag to chip off. Something in the 130 to 170 amp range would still work off a 110V outlet and provide enough amperage to weld up a decently strong blade.
Also I'd check the yellow pages of Your local phone book for "Steel Distributors & Warehouses" Call a few of them and see who has the best price, and if they have the equipment to roll the sheet for You.