There are a lot of options in the 70cc range.
Big valve with screw-in studs are most popular.
670 / 16 / 62 / 48 / 12 / 13
You'll be around 10.5 - 11.0 CR depending on bore size - milled depth - piston to deck clearance etc...
Are you wanting correct 1969 heads ?
Here is a website with good head info :
http://www.wallaceracing.com