Here are my thoughts/suggestions.
For your lowering blocks, drill a bunch of lightening holes if you would like to take some weight out of them. Other than that, they look like they'll serve the purpose just fine. For an example, look at a 1-2-3 block.
As for lowering your front valence, I don't know how that would look as the fender sides of the valance are molded to the contour of the fenders. Just my opinion, you might be served well by a Cobra II spoiler as it will direct air upward toward that opening if you choose to mount there.
Your wheel spacers should work just fine. It's hard to tell by the pics, but the meat of what holds the spacer onto the disc/axle should suffice. If you're looking at the counter-bore of the bolt holes, that really won't matter that much as it is just dead space anyway. If you're concerned with concentricity of the wheel, it sounds like you have a competent machine shop more or less at your disposal, have one of them make a sleeve with the ID to fit the hub of the disc/axle and the OD to fit the hole in the spacer with enough of a lip turned down to the OD of the hub to engage the wheel. That should locate the spacer AND the wheel without depending on the bolt circle as your locator.
Now, the fuel pump. I don't think that you would need something with that much PSI in a carbed application. The needle and seat in a carb could be overpowered by the excess pressure. IMO, what you need to be looking at is flow, not pressure. Someone more versed in this respect can probably lead you in a better direction than I can.