It seems that many of the inliners with headers and an aluminum manifold have hot engine water plumbed thru the floor of the plenum. I would think that to be a big help in a cold climate for a modified six. You can see some like that in this thread
https://67-72chevytrucks.com/vboard/...d.php?t=276823 post #108 shows it clearly. And post #124 seems to have a water heated spacer under the carb.
Edit: I wouldn't hesitate to buy a Summit branded part. I imagine they'd have your back if it was detective.