Are 99 SummitX 670 cylinders the same as a 97 Summit 670

No, not the same

Different cyls, pistons, and head

The heads have a different dome and squish, requiring a flat-top piston for the X/H.O. engines. You can mix and match as long as the pistons match the head used. The cylinders are actually the same, the only difference being that the X/HO cylinders have a window cut into the rear cylinder sleeve allowing a straighter shot into the rear intake transfer..... From what I have measured, the actual ports retain the same dimensions. The cases are also factory tunnel-ported in the X/HO motors as well....

You could take a standard cylinder, and notch it to match the X/HO cylinder. Quick easy job for a machine shop, as it is really just a round notch cut into it. You could do it yourself, if you are careful, with a die-grinder.

If you insist on an X/HO cylinder, I think I have one laying around....

The heads have a different dome and squish, requiring a flat-top piston for the X/H.O. engines. You can mix and match as long as the pistons match the head used. The cylinders are actually the same, the only difference being that the X/HO cylinders have a window cut into the rear cylinder sleeve allowing a straighter shot into the rear intake transfer..... From what I have measured, the actual ports retain the same dimensions. The cases are also factory tunnel-ported in the X/HO motors as well....

You could take a standard cylinder, and notch it to match the X/HO cylinder. Quick easy job for a machine shop, as it is really just a round notch cut into it. You could do it yourself, if you are careful, with a die-grinder.

If you insist on an X/HO cylinder, I think I have one laying around....

Zachmandu do you still have the cylinder I'm actually looking for a pair of cylinders for my 98