I know you asked for a "good" description... a pic would be best, but I don't have one.
The pumps are identical, the pulley is identical, the pump resevoir is identical, except for the routing of the low pressure return line nipple. The only difference is the shape of the bend. On the small block, it routes above the high pressure inlet fitting. On the b/b it routes about 1" below that fitting. If you look at the assembly manual RPO N40 A8 (page 405) you can see the difference. If you don't have one, I can fax or mail you that page.
I took a small block, and carefully re-bent it for my b/b. I put the high pressure line on, and bent the nipple susch that it would route correctly, and not rub on anything.