340 radiator

You can make them work with some modifications.
There is a slight difference in hieghts of tanks and cores between the 70 up square tops and the earlier bubbletops.
The earlier cars used a shorter water pump, and the fan tips were clearanced to match the bubble tops.
Shifting the radiator brackets back so the top tank sits further forward buys some additional clearance when putting a squaretop in an early car.

* The best way for fit is to use the shorter, earlier water pump and the earlier 'bubble top' radiator.
* Second best IMO is if using the a '70 water pump, to have made up a combination radiator - '69 and earlier radiator modified with a left side outlet lower tank.
+ Do some trial fits. Core and lower tank height together need to be shorter than a 70 or the hood may not close. Expect a shorter fan spacer or shorter clutch fan may be needed.
* Third best is to use the '70 up water pump and radiator and expect to modify mounting brackets including resoldering them. Custom or modified fan shroud will be needed if using a fan shroud.

Use a torque strap if the fan or clutch is anywhere close to parts of the radiator. You can probably guess how I learned this as well as the stuff above..

Squaretop with mounting brackets shifted back (in a '67 B'cuda)
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Fan clearance acceptable, good hood clearance. MP 5 blade fan & fan clutch
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Fan clearance of just over 1/2" with a combo '68 top/70 bottom. Original fan and Hayden 2705 fan clutch.
Glenray68-70b-092.JPG

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