I´m in Bolivia, South America, the access is not a problem since the work is in a gas plant that has all the facilities to work safely, the hot tap will be performed vertically, overhead clearance isn´t a problem and you are right about the weight of the tapping machine. We will verify the condition of the header line by measuring the actual thickness (U.T.), we also have the initial composition of the header pipe.
I´ll complete my profile info…. 
Thanks for your interest!!!