mounting miata seats in a spider

[JHahn22@domain.elided]

Hello everyone,
I'm in the process of mounting Miata (or some other plentiful, small seat) in 
my 87 spider.  As always, things have gotten complicated.  It seems as though 
someone else had these seats out, and when they put in the passenger side 
seat, the outer rear seat screw was put in wrong.  I'm not sure what they 
did, but even after drilling a hole in the rusted seat pan, in order to get a 
real screwdriver on the screw, I couldn't get it to budge.  The bolt ended up 
breaking off in the hole when I used vise grips around the head.  I then 
drilled a hole and tried to use an EZ out bit.  Not too mention all the PB 
Blaster I've sprayed on it.  
My question is, can anybody think of any reason why drilling a hole in the 
floor pan in the proper place to mount the miata seat rails, and using a bolt 
and nut with a stack of washers under the rail, and perhaps a rubber bushing 
of some sort underneath to keep out water, would not work to safely mount the 
seats?  Should I use somekind of reinforcement on the seat pan, or is the 
sheet metal strong enough?
Also, can anybody think of a nice, supportive, small seat like a miata seat 
that has an adjustable headrest?  It would make the shoulder belt guide a lot 
easier to rig up nicely.
If the gentleman that emailed me pics of the tan miata seats in his 70's 
spider is still on here, could he please contact me off digest?  I seem to 
have lost your email address.
Thanks for any ideas on this one,
Jake Hahn
Bryan, TX
87 Spider
87 BMW 325i
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