Afaik the 817cc engine was only used in the USA up to end 1969
to avoid having to meet emission regs at the time.So your 1970
built example should (?) have the 903cc engine as this was
introduced to all other markets when the model designation
changed from 'Spider' to 'Sport Spider' in March 1968.
Can you have someone check if the rear badge says Spider or
SPORT Spider?(if it says Sport Spider its a 903cc).
Can you check the engine number suffix (perhaps its on the title
or other documents?) and post same on here, someone is sure to
know which engine this indicates. IIRC the engine number is
stamped into the engine block above the timing chain cover near
the rear engine mounting bracket.
Al.