Just curious how you have determined the head is bad? They are prone to cracking if you overheat them, but you might also just have a bad head gasket.
Got Oil in the coolant?
Coolant in the oil?
Compression leaking between two adjoining cylinders?
Miles on the engine?
Most people have had good luck with Clearwater Cylinder head. $251 sounds pretty good as long as it's a quality job. However, for about $350, you can get a NEW casting from Clearwater and it will come with new valves, springs, seats, guides, ect. You'll just swap over your cam and rockers/shafts. If they plan to keep the truck for the long term, and assuming your head is in fact bad, I would be inclined to go new versus reman.
You might want to pull the head first and see what you've got. You might only need a gasket. Here is a thread I put on Mazda Trucking with some other tips and things to look for "while you're in there" on a head / gasket replacement job.
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One final thought. Overheating is the most common cause for gasket & head failures. So if and when you make this investment in a new head, make sure your cooling system is in top notch shape; especially all the little coolant lines that are under the intake manifold and wrap around the back of the engine. These hardly ever get replaced but when they fail, they will leak your coolant out just as one of the large radiator hoses will do. Point being: While you have the head off is the most convenient time to replace all of these hard to get to hoses. I also highly recommend going with OEM Mazda hoses are the are molded for a perfect fit. There are also the metal lines that are prone to rusting. So be prepared to replace them if needed. The one that returns the coolant to the water pump has an o-ring (probably 21 years old now) so now is the time to replace that one as well, whether the metal line is rusty or in need of replacement or not. Here is a pic of a new one on a new pipe, and a 23 year old pair. That o-ring will have lost almost all of it's elasticity. And if the pipe underneath is starting to rust, then you have a leak waiting to happen.
And here are all of the aforementioned hoses and lines.
A little more information that you asked for, but if you can survey what parts you'll need before you start the job, you'll be able to get it back together quicker... or won't be in the predicament of putting it back together without the new hoses because you don't have time to order them and wait for them to arrive.