360 converter

What year 273? If it's the original 66 they had an 18 spline input shaft. 68 and newer 904's (you didn't specify which trans. but that's what came behind 273's) had a 27 spline input shaft. There is also another issue, the torque converter pilot hub (the part that engages into the crank) is smaller on the older units. Your easiest and most cost effective way to go is to keep the original torque converter, buy a pilot hub adapter from Torqueflite Patty and get the B&M 360 balance plate.