What does this mean? Radiator question

I've been researching the numbers on my radiator (2898067). According to the table on this website, here is the info: 68, A body, 22", 225, HI ALT-A/C.

http://www.rosevillemoparts.com/reference_radiatorguide.php?SID

My question is, what does HI ALT-A/C mean? A/C is obvious, but what does HI ALT denote?

Also, will any 22" a-body shroud fit this radiator? Where do I get one??? This 340 is running waaaaaay too hot.