I don't think it was brass but admit it was decades ago when I last saw one. Regardless, using a softer material (or equal) to
the cast aluminum manifold itself makes sense as the tubes were a press fit. A too strong tube could, with heating/cooling, cause a crack.
Couple of pictures below of one I just finished for another guy. The lighting in my shop makes the casting look yellow, but really its not. Also please excuse the one hole that I didn't get deburred yet on the closeup of the port. The pushrod tubes are 3/4" OD 0.062" wall aluminum. I squeeze them in a vise onto an arbor with the correct oval shape, then use the arbor to pound them into place in the pushrod holes...
Didn't Ford use brass tubing in the originals? Might there be some metallurgical reason to use brass?
