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And do it right....Should be roughly a pinky finger between the bumper and the tip befoe the flare so ~1/2". Also the tail pipes when viewed from the side should tuck tight against the trunk floor. Not touching of course.
It's not clear from the wording of your post whether you're looking for "original" tailpipes or if aftermarket would be acceptable. In terms of routing accuracy, you can find many options available in a Summit catalog (Pypes, Flowmaster, etc.) They'll work fine and will, in almost all cases, be mandrel bent (unlike the "originals") and are offered in plain steel, aluminized steel or stainless and various diameters. Once installed, only a diehard enthusiast would know they differed from "originals".
Obviously, if you're doing a correct restoration and want/need original style tailpipes, these won't do but all of the parts suppliers offer "original style" kits. I'm not sure how good/accurate those are. Gardner has a good reputation but I've found them to be somewhat strict and un-flexible when I've inquired about purchasing portions of a full kit. I'm not sure whether places like Year One or Parts Place offer just the tailpipes but I'd have to think so.
By the way, I've always liked your tagline. I have a '69 442 and am with you on the 400G!