you could pick up some cheap "computer ""case"" fans". and mount them behind the core, so the wind blows through the core. computer case fans are cheap little plastic fans, that have 4 holes one per corner. some of the fans come with 2 wires coming out of the fan while others 3 wires. to make life easier just get a 2 wire one. gennerally they have a computer plugs on the fans. you can cut them off, and install a toggle switch. double checking
Newegg.com - Computer Parts, PC Components, Laptop Computers, LED LCD TV, Digital Cameras and more! ((do search for ""case fan"")) if details state it has a 4 pin connector, most likely it only has 2 wires coming out of it. if it says 3 pin connector, then most likely fan has 3 wires coming out of it.
also take a look at "pci slot fans" you can get 2 fans side by side. but be carefull you may not be able to drill any spots to get a bolt or some sort of wire through to mount them.
red wire on fan to red wire on tractor (positive side of battery) put i don't know 5 amp fuse between black cable (negative side of battery) then toggle switch, then black wire on fan.
if ya want a couple fans then just run red wires together, and black wires together. from both fans. at a certain point you may need a bigger fuse. maybe 10amp or 15 amp fuse. depends on fan.
or perhaps hitting the auto section of various local stores come summer time. to find them 12v fans that plug into cigerate lighter. during summer time you can find various fans that clip to about anything, cut off the ends, and attach a fuse (depends on fan/s) then toggle switch. and just like the fans above.
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perhaps getting a old gas water heater tank. and taking out the coiled fins in it.
junk yard, walk around, till ya find something.
you might take a look at floor heaters that run off of a boiler, (ya generally see in old houses) you might find one with a bunch of small fins, that fits fairly nice across the entire wind shield.
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you could prolly run a couple cores in series, outlet from one core to inlet of other core, if the water pump can handle it. but you might find it better. to run 2 cores in parallel. to control how much coolant goes to each core. ((other words hotter for front, cooler in back, or vice vs or same amount of heat or be able to turn off each one if ya ran them in parallel)) running in parallel will most likely give you a little more heat as well.
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because the cores are being mounted in the ceiling i would ""take very special care"" and make sure that you can place a tee in the highest area of all the lines including the piping going through the cores. and then drill a hole and go right out through top of the cab. then put a valve on top of the cab sticking straight up. ((to each his own, use a little spray foam, if it was me, ""great stuff"" in a red can)) or perhaps a little silicon. between roof and pipe running up and out of the roof.
then placing a valve on each inlet/outlet lines coming from engine and place valve either at the floor or under the floor ((other words some place low))
the 2 low valves, you will need to close, then you would need to climb on top of the cab, and pour antifreeze/water mix. down the top valve. this will allow you to burb any air out of the lines and cores.
((hint get a couple fittings to goto a 4" plastic pvc pipe)) to create a DIY funnel that fits on the valve above the cab. it may seem silly, putting hole through roof of cab, just for a valve. but it can save ya time and problems removing air. from the lines.
side note pending on how you run your coolant lines up to the cores. you may need a another tee and valve pointing up and going through roof of cab.
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brass gas valves at most local hardware stores could be used as valves. i would assume.
