Ummm... it's been a while since I worked on a FFS freewheel and crank (35 1/2 years?) but I think you need to pry off a giant circlip that holds the chainrings to the freewheel unit. It's on the outside of the chainrings- that is, you could remove the chainrings without taking the cranks off the bike. It's not necessary to remove the freewheel unit from the crank (that requires a special removal tool).

I think... I wish I could find a picture from the old Schwinn repair manuals. Those things were amazing.