There is a kit manufacturer who is doing a copy chasis frame of the original RS200.
Cannot remember who it is but I read it in one of the kit car mags last year.
They bought the original moulds from another kit company that went under who had aquired them from Reliant some years back.
Reliant used to make all the body panels for the original RS200 as they were considered experts at fibreglass body's at the time.
The Seirra will be needed as a donar as the original car uses the Seirra dash and windscreen anyway.
Try e-mailing one of the kit car mags for further info
I'm sure they will tell you