That 18268 (and the patent numbers) will appear on other Bendix boosters as well, not just the hard to find 70 E booster. I believe 18268 is Bendix's vendor code for Chrysler. The 70 E booster should have 8550 on it, that is one sure way to ID it. And the football shaped indent around the pushrod is the other thing to look for. The Chrysler part number and a date code will appear along the top edge, hard to see sometimes with the paint and sometimes faintly stamped but it will be there. I believe there are a few different possible Chrysler part numbers, post up what you find on that top edge and we can confirm.