With so many people converting to LS engines these days, I thought this would be useful for many of you! I found this out during the LS swap on my '78 Chevy.
Murray makes an over-the-counter replacement radiator that is LS swap ready! The part number is 433161 (I believe I purchased this at Oreilly's), and it includes a 1/8" NPT port between the transmission cooler ports, which is an identical position that the steam line runs to from the factory. All you need is a 1/8" NPT to 1/4" barb adapter, and you can run a 1/4" rubber line directly from your steam line on the engine to the radiator!
I purchased these from Autozone. 072010 is the 1/8" NPT to 1/4" barb adapter. 071910 are block off caps for the transmission cooler.
I hope this helps someone!