Actually my post needs a small correction--the barbs on the heatercore are 1x5/8 and 1x3/4, not 1x5/8 and 1x1/2, like I said earlier. Those measurements I'm sure of.
But, it looks like I'll have to re-measure the rest of it as well, since my specs don't match the heatercore4u.com ones. Maybe I just can't operate something as fancy as a yardstick...