If you use them together (the 8" & ED80)
GS 8" - 9.5kg
ED80 - 2.7kg
Finder - 450g
--------------
Total - 12.65kg
Plus EP, Camera, tube rings.
You will need a mount that can carry 15kg min.
The HEQ5 Pro has a load capacity of 16kg
http://www.opticalvision.co.uk/documents/71.pdf