After drilling a location hole from the bottom I removed the seat and MC, cut out the access hole and put the seat and MC back in place.
Attachment 64906
I cut a piece of 16ga sheet metal to overlap the hole all around, and after sanding the top side of removed plug smooth and roughing up the plate I bondo'd the two together. The plug keeps the access plate located, and also fills in the hole from the bottom side. This is the cheap and easy way to do an access port, and with the bed liner material in place it becomes all but invisible from below.
Attachment 64905
Sitting in place the cover will be underneath the carpet with a fold back panel to allow access, held by velcro tabs.
Attachment 64904
The only thing left to do is to swap my power brake master with the shallow dimple in the piston for a manual model that has the deep recess. I was able to re-shape the brake line from the front to use in the back position, and only needed to buy one 20" line and form it for the front. Problem solved.
I talked to my guy in Florida who does Fiero & Mazda seats for a myriad of vehicles, to see if he might possibly have patterns for Fiero seats sans headrests. To my surprise he pointed me to a page on his web site, and scrolled me down to a picture of a '62 Corvette with Fiero seats. He quickly explained how I should go about cutting off the headrests, and told me that it was as easy as taping in a length of cotton batting atop the cut edge to fill out the top of the seat back, and they look like they were made that way from the factory. With that advice I chopped off the headrests, and did a test fit of the seats. They're cozy, only about an inch or two between the bolsters, just enough room to reach the E-brake handle.
Attachment 64907