someone else will have more visual familiarity with what a '68 or '70 frame should look like but, until then... is that all metal, or is there bondo in there? i thought there should have been two top tubes? something like this (just found this on google):
either way, maybe someone welded in new gussets since more of the headstock would have been visible after the chop. hard to tell from your whole-bike picture. so it doesn't necessarily mean they even changed the rake, let alone swapped in a new head tube. but maybe they did? what's visible of the the triple trees look normal (including the bent steering stops). can you see any casting marks in the yokes?