This refin project is done and here are the pictures (thanks, Rob). My 1965 pre-CBS Mustang had been refinished Dakota red when I bought it. I wanted the slab to match the neck and headstock. The Poplar posed some real challenges to this goal...the slab's three pieces of wood, two are dark brown, and the middle piece is blond.
Fortunately I got helpful information from folks who know what they're doing. For those who might be interested, I'll be posting a detailed description of the step-by-step...mostly stumbling...process I followed, including a couple of refinishing tricks I learned.

When stripped, it turned out the Poplar was dark brown and blond. In this photo after the refinishing, you can sort of guess where the brown was darkest.
Butternut gel stain lightened the brown.

Autumn gel stain darkened the blond.

Fender Neck Amber (from Guitar ReRanch, Texas) then brought the colors even closer together. This photo makes it look like there's some red left in the wood, but it's just the lighting and my poor photography.

And a final coat of Nitro with 20% amber tint (Guitar ReRanch) sealed it. After I took these photos, I sprayed a bit of the Nitro on the trem bar tip and it now matches the pickguard. So I think I'll gently wipe a bit of that on the pickup covers, too.