Just go on to Amalcarb'co'uk and use the model selector, a 1970 Venom gets youhttp://amalcarb.co.uk/carbspec/carburettor/spares/id/5872/
Carburettor Specification: 930/29
This carburettor is built to the original specification and comes supplied with:
3 Cutaway Slide
270 Main Jet
106 Needle Jet
The pilot bush would be 25, if you have a premium then the pilot jet is the 17 (same size as the 25)
As today's fuel is not the same as in 1970 then some adjustment could be needed.