Greg:

Let me take a look at mine tonight. I think you can simply remove the site glass manifold assembly (along with the brackets that attach it to the frame) and reinstall everything on top of the frame. Then, before you reinstall the glass, pop the tall top on and mark it for centers on the site glass and cut your holes. The rubber gasket is held on with the SS Trim and two screws. The manifold holds the site glass in place. The glass just projects thru the top.

Like I said, I'll look tonight, I've got a few of these and have both short top and tall top ('cyclops') versions (and a 'Blue Sonoco' ad top pump!). If need be, I can shoot you some digital images of the arrangement for reference.

Later . . .

Jim

[Linked Image from cruisin66.com]