I recently swapped a 408 windsor stroker into my 68 mustang in place of the original 302....I was concerned that cooling the new engine might be a challenge since it would be over twice the horsepower of the original engine!....Luckily my car came with the heavy duty cooling package since it had air conditioning...The heavy duty cooling system is basically nothing more than a 3 core big block rad with the lower outlet on the passenger side to match the early small block water pump....I wasn't sure if I should replace the stock style rad with a 4 core unit or try swapping in a light wieght aluminum rad with supposedly superior cooling....After doing some price shopping the Northern Universal fit aluminium rad was well over $100 bucks cheaper and the dimensions sounded close to stock so I thought I would give it a try....The stock rad measured 21 X 25 3/8ths while the northern was 19 3/4 X 25 3/8ths....
The northern was advertised as a 19X26 so it was a bonus that it actually ended up being the exact same width as the stocker and not the full 26 inches as advertised...Room is tight here on an early mustang between the battery tray on one side and the voltage regulator and wiring on the other.
Now that it appeared it would fit in the car ok I had to figure out how to mount it...Again I was very lucky to have had the big block style rad in the car originally as it has similar style bottom mounts to most cross flow rads..These little mounts bolt to the A frame at the front of the car and can be easily added to normal small block cars whose radiators actually bolt to the front radiator support
I did have to modify the mounts a little since the thicker end tanks on the crossflow rad make contact against the rad support and make it sit towards the engine a little more than the stock rad..I simply removed the mounts and bent them flat and then rebent the ends back up giving me an extra 1/4 inch or so of flat length for the rad to sit on..The stock rubber insulators were now too short to fit back into the stretched mounts so I had to go to the local wrecking yard to find some that would fit....I robbed a pair of lower rubbers out of a mid 80s cadillac that were plenty wide...I applied some weather strip adhesive on them to help keep them in place and stuck them on the steel mounts....
Now it was time for the top mount which in my case is a clamp on type big block style mount that bolts into the front of the rad support along side the hood latch...It required the same widening treatment as the lower mounts since the stock rad actually narrows in on the top tank for the mount to fit into..It was a little harder to reshape the ends of the mounts but I managed to get it done with a vise and ball peen hammer.
I wasn't entirely happy with the overall look of the top mount but it was functional and used the stock parts..I did need a longer piece of rubber just like the lower mounts to span the extra gap..
The outlets on the nothern rad are the same size as the original and amazingly the stock 302 rad hoses fit perfectly even though I switched to the drivers side lower outlet for the 408....
So how does it work?....Well I have been very pleasantly surprised..With a 180 degree thermostat and an ancient clutch fan the engine runs right at 178 degrees even on extremely hot summer days...Sitting still in traffic on those very hot days will see the temp slowly climb to around 190.. I'm sure this would be easily fixed with a shroud which is on the "to do" list.. I am going to switch to an electric fan with a built in shroud in the future and probably fabricate a nicer looking upper mount like a later model mustang that would cover the whole top of the rad...
Update...I finally got around to changing my upper rad mount..I simply used two short pieces of threaded rod through the original holes in the rad cradle and into the top edge of the rad...I put a nut on each end and covered it with a piece of stainless steel...

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1968 mustang..408 windsor.Vic jr heads and intake.Pro Systems 950HP holley, 1 3/4 hooker super comps,Custom CI solid roller camshaft,Probe shaft rockers, 4 speed with 4:11 detroit locker.