If nothing else available in blueprint form for an OT1300 (Periscopo) chassis , perhaps an enlarged copy of the drawing of plan,sections/elevations of a chassis and body as well as two informative photos at pages 276,277 of the book ABARTH the man, the machines, author Luciano Gregio published by Giorgio Nada Editore srl , in 2002 , ISBN: 88-7911-263-5 could be helpful. The scale drawing dimensions wheelbase, track,length,width and height and shows mechanical and chassis framing and if enlarged appropiately could be used for reasonably accurate sizing. Good luck in your search and please let me know if you are able to locate a blueprint.