A 1969 3 or 4 row radiator and the 69 fan shroud along with a fan clutch and fan gets the job done quite nicely.
First you will need to trim about 1-1/2" from each side of the hole in the core support. In order to redrill the mount holes the radiator needs to be temporarily spaced off the frame about 1/4" Drilled the new holes for the 4 bolts holding the radiator to the support. They should be in line with the existing holes that were removed when the core support was trimmed. The core support may have to be adjusted forward about 1/4" to allow for the radiator's extra thickness. The fan shroud bolts directly to the radiator, after drilling 4 mounting holes. If you use a 3 row radiator, the holes are already there. Then the clutch fan and new clutch can now be installed.
You may have to make some new brackets for the A/C condenser, if you have one, in order to move it about 1/2" forward and the new mounting holes will need to be drilled in the core support.
Some quick dimensions to help you make your sizing decisions
70 Mustang Radiators
65 Mustang Radiator