That's all cool, I don't see where it says those retainers will ensure a 1.800" install height. I went to a machine shop with a set of heads with a set of the retainers in your link and I got 1.78x" from the spring seat to the retainer. In chatting with others, I heard teh same measurements that I found.

I'm not positive on which seals give more clearance, but I've heard the ZZP ones do. And those look just like FelPro seals.