I am just trying to figure all this out. I pulled the original heater core out of my late '71 and the core is a full 21/2" thick, not 2". It's taller and wider than 280 ones on the market. So why won't a 280 one fit in my box? I wish I could find one to try out but someone should know. One difference I see is the 90deg pipe on the 240 is angled upward while the 280 angles straight back. I would think this could be worked around.