I had this problem to a much lesser degree with my "no-name" rockers that I had before, but I wouldn't have thought the Comp rockers would be a problem.
So, even if you leave the pushrod end of the rocker up higher it still hits the retainer? It looks like you have more interference, and would end up grinding away a good chunk of material. I don't know what the effect would be, but I would be scared to do it too.
Not that this is good news, but I think the PVS (Miller Engineering) rockers that I just bought are clearanced for 1.55 springs. If you look on the website you can see how the underside is clearanced.
FYI: Competition Products has them priced really nice at $159 a set for small block and only $139 for big block. And they are nice, seem to be nice quality! Lifetime warranty on them as well!
Can see them here: http://www.mid-lift.com/PVS-PA.htm
If you click home at the top, then click on the STUD-BRIDGE will see the "STUD - BRIDGE" which is a wicked stud girdle. Talk about cinching everything up tight. It's a different design.
I like that site, really pretty interesting concepts.