Are all 273 V8's the same?

A 65 will bolt up to a 66-67: it was 68+ that had the larger crankshaft convertor snout receiver. Your initial question was would a 66-67 fit in a 65. The answer is yes as were only dealing with external engine mount bosses and crankshafts. Don't let the haze of year to year changes internally cloud your decision.