Replaced the long ago blown and bypassed heater core in my 66 coupe (289 no A/C) with this one. It is identical to the original, a perfect fit, and seems to be of high quality. I suggest replacing the hoses as well since you have to drain the cooling system anyway. Mine required about 7' of 5/8" heater hose.
When I first rebuilt the heat system, I used the aluminium replacement core. Was not able to use the end caps with it and it ruptured after only 3 months of use. Bought this one and it fit perfectly. Used the end caps and its been 3 months and no leaks! haha