So aside from M40's as orig. equipment in a '68 & up w/ L78 or better, no other '65 to '69's had this feature...but all '70 & up M40's did? .
And what about the 6-bolt torque converter M40's in commercial trucks...would they have had this pre '70? .
Where I grew up (have I yet?) apprentices were sent for a "Long Stand" and you were told to be specific that a short one just wasn't sufficient and stress that you really wanted the longest one available! . It took a while sometimes but after standing there waiting and waiting, it usually clicked...if it didn't, the guy was a marked man! .
~ Pete