67 V8 radiator in a 66

Sure looks it. Time for tape measure, paper and pencil.
When I've had to get replacement radiators, I've used cardboard to trace over the mounting flanges etc of the radiators and the openings. It helps when figuring when figuring out what's different.

upload_2020-3-20_8-19-52.png
And this - which is a 68 with 70 bottom tank.
IIRC the 70 tank is taller than the 68-9 tank so the core has to be shorter.
upload_2020-3-20_8-15-59.png

First try didn't fit.
upload_2020-3-20_8-21-8.png
Measure this
upload_2020-3-20_8-20-33.png

and then these

upload_2020-3-20_8-18-9.png

upload_2020-3-20_8-18-37.png