By "crossmember" are you talking about the transmission crossmember, or the entire front frame bolt in section?
if you are talking the entire bolt in front frame section, Chrysler changed how they were bolted onto the body shell. My guess would be, 66 & 67 and then 68-70 and then 71 -72 would interchange. The spool motor mounts came along in 73 but those might fit up into the downsizing after 78. The demand for the "big" cars dropped around the gas crunch in 74, Chrysler didn't change much under those big cars after the demand fell off.
Transmission crossmember? 68-72 then 73 on. My guess.
Now that you say that I think you're right. It wouldn't be a roller without the front frame. If it really is the trans crossmember, i think '65 to '73 should work.
