Dont be scared of monocoques as long as you leave the structure alone and rebody over it it will be fine.
The MR2 ferraris have been doing this for years and i built a MGF based car before this - a rare beast a Blaze
Unbolt the front wings - fit fibreglass flip front - add fibreglass panels to the sides and rear arches - blend and paint.
I know it sounds a lot like the roadster build
