Hi ufo17, the Triumph Herald wheel base is 91.5in or 2324mm and the Triumph Spitfire wheel base is 83in or 2110mm.
So the Triumph Herald would be very close to your Locost wheel base.
You could get the extra needed with a longer bonnet but as these bodies are only single skin it would not be to much of a problem the add the little extra some where else
It you want a body please PM me.