I've tried to Google this all afternoon but I'm going round in circles without finding what I want. Where can I find info about stock Type IV measurements (piston size, stroke, CR etc etc)? And info about what common upgrades are available (e.g. bigger cylinder measurements)? Thanks!

http://www.tunacan.net/t4/reference/displace.shtml 

hth

also try air cooled net and look in there shop and see what is there

Also try Type 2 .com

http://www.type2.com/library/library.htm 

Thanks guys, great links.

http://www.aircooledtechnology.com