[Safari Larry]

Pontiac heads are interchangeable side to side but 1957-59 tubes are not. Looking at the tubes from the end, they are mirror images of each other (see attachments). The tube can be inserted in the head only from one end and the flared end needs to be in the front. If you moved a left head with left tube to the right side then the flare would be at the back of head which would be incorrect.

The 1955-56 tube can be inserted in either end of the head. If you moved a left head to the right side then you would need to remove the tube and insert it from the other direction -- so the flare is in front.

I'll take a look at my 56 heads today, didn't get a chance to yesterday, sometimes life gets in the way of important stuff.

[Safari Larry]

I diddled with the 56 heads yesterday and got one of the tubes out without bending it up too badly. Can't get the the other out, it is stuck.

I tried a 57 tube in the 56 head, it would go part way in but a rib near the center of head stopped it from going in further. It was same inserting it from either end. It might be rust buildup in the center two ribs that prevented it from going all the way in, not sure about that. Those inner ribs are difficult go get to.

Some photos attached of tube in 56 head and 56/57 tubes together for comparison (57 is cleaner).

Bill, I think your GMC parts book is incorrect.

[Bill Hanlon]

Originally Posted by Safari Larry

Bill, I think your GMC parts book is incorrect.

I agree. Thanks for looking.