You're converting a 1:72 scale Su-27 into a Su-34 ??
What for - when there is the Italeri/Revell(and now Tamiya) kit of the Su-34 ?
As for David's request - the only vacform Flanker canopy that I know of is the Su-27UB one from Aeroclub - there aren't any available for Su-27's or Su-35's.
Don't for get that the Su-35 windscreen has an offset IRST ball - the ball on the Su-27 is centrally mounted.
Finally - why go with the Berkut (aka Nakotne/Encore/Eagle) kit of the Su-35
- it isn't very accurate. I always use the Airfix kit - it's a crap kit - but at least IMHO, it is an accurate model from which to start conversion to a Su-35 - see my articles on Linden Hill's website at :-
You could alos check out my survey of all the (currently) available Flanker kits at :-