#48 heads (as posted elsewhere) had heavy-duty dual springs where the #62 used standard-duty dual springs.
Both #62 and #48 are rumored to have been used on Ram Air 3 (or 400 HO) motors. This, however, may not be accurate.
#48 heads were also used on non-HO 400 and 350 4-Bbl engines when fitted with a manual transmission.
So, #48 does not mean Ram Air (or HO) only.
Q, I've heard that about the #48 heads as well. I wish my convertible had it's original engine to verify the rumor. That's one of the reasons I put #48 heads on my 'bird last year. The other reason was having a miss-matched #16 & #62 head on the block.
