I have 3 acres of way over grown pasture I have to maintain now.
Depends on just what's growing, and whether you're willing to do it in 2 or 3 passes, or just hog it all in one pass.
Is it only grasses and small (less than 1") saplings? If so, then a pull-behind finish mower will work, PROVIDED it is modified to allow for 12" or so cutting height. Then could lower it down to about 6" to 8" cutting height. Then, if you needed to go lower, you could do so even with a box-store riding mower.
It all comes down to time, and what sacrifices you're willing to accept.
...Back in the day, grain trucks had smaller gas engines and were geared low with slow speeds. Nowdays, everything has to be faster, so older grain trucks are pretty much useless. Doesn't mean they can't do the job -- only that they can't do the job as fast as newer and more powerful trucks.
Up here, our "grasses" are native field grasses and grow to 6'+. When we first bought the place, all we had to work with was a riding mower. Grasses kept saplings at bay, but the mower still struggled with the tall, wet grasses. Took 2 forever's to get it knocked down, but eventually we won.