Here's the deal. These engine's are sensitive to overheating, and the slightest running hot condition can blow a head gasket on one or more cylinders. It definitly sounds like this is the case, with the smoke from the exhaust, rough running, etc. But, now the question is - when did the head gasket blow. Normally on this engine when the water pump 'knocks' it is also leaking badly, letting all the engine coolant fall to the ground. If this were the case the coolant will have been lost at a rate which could have immediatly cause a localized overheating condition at a weak point on the head gasket, therefore the engine may have not run too bad, but after the repairs the gasket could have completely blown, and the shop just got caught in the middle of an imminent failure. Or, it's possible if you have no overheat condition, and no loss of coolant; that the repair wasn't done correctly. The cooling system was not bled properly and or the engine was not monitored and allowed to overheat causing the gasket to blow. So this concern can very well have been the result of a bad mechanic, which i've seen a dozen times on this engine. Regardless, the problem leaves you stuck and with a large repair ahead of you. So if you feel the repair shop is responsible, I would have the vehicle towed to another - more reputable- facility, to complete the head work.

-Rip