The 80cc Metra kit will get you to actually 74cc, correct? Also, what is the spring for in the 80cc Metra kit? Here is a link to a pic. If you enlarge the pic there is a spring with the kit. I looked on another site that had the spring listed in the components that are included with the kit.
http://www.1977mopeds.com/catalog/index.php?main_page=product_info&products_id=99