Ram tubes from a naturally aspirated Hilborn setup (in this case, this set came off of a '59-64 371/394 (NOT '57-8 371) injector). Set of 8 in good condition and not beat up at all. 2-1/16" I.D. with 2 screw bosses at the bottom and a bevelled lip on each for pairing together on siamese-port engines like the Olds.
The center-center distance of those two mounting holes is 2-1/2", and the total length is 5-13/16".
Original type and not the new stainless ones Hilborn currently sells (at $320/set!).
May very well fit Hilborn setups other than for just the 394 Olds... check your measurements.
$90 plus mail. If you have beat-up or missing tubes, then this might be a really good time to pick some nice ones up.