To answer the "legal" question about running old CA plates on replica Speedsters...
What I have done (3 times, actually) is order an Environmental Plate from the DMV with the configuration I wanted - in the case of my Black JPS (pictured below), I ordered "SPDST." Three months, or so, later, the state of CA sends you the current blue-on-white license plates with "SPDST" on them.
In the meantime, I go to the LicensePlates.tv website and order a classic CA plate - in this case a yellow-on-black one - in the exact same configuration "SPDST." Then, when the real plates arrive, I put the MONTH/YEAR stickers on the replica plate, mount it to the car, and stash the blue-on-white CA plates in the trunk.
So, is it "legal?" Strictly speaking, no. But, I've been stopped a few times by the authorities and never once was the replica license plate an issue - because...the configuration on the replica plate is identical to the plates actually registered to the car. I'm not saying it wouldn't ever be a problem for you, but it hasn't been for me. YMMV.