Main Vents

Stuart_7

Friends, I need some help. I've got 1912 one pipe steam that needs new main vents. There are two mains that loop the basement then drop back at the boiler. One is 2 inch x 57 ft.,other is 2 inch x 35 ft. There is a third run out from the header 2 inch x 18 ft. that then has a 1 1/2 inch x 11 foot riser feeding two bedrooms. This last has relied upon the rad vents only and they need some help. I plan to put a vent at the top of the riser.
How much air is there per linear foot of 2, 1 1/2, 1 1/4 inch pipe? What three vents would you recommend? Thanks