As long as you can find two survey or corner markers, and are 100% sure they are on and correct then using a little math, and some really long measuring tapes will get you in the ball park.
If you don't want to pay for a new survey then back off 10 feet from where you think the line is and post away. I wouldn't try to post on what you think the line is because in my experience you can be several feet of using a regular GPS, compass, tape, and/ or your best judgement.
I have all but one corner marker, and the missing marker is an actual measurable distance along the road so its not really a huge deal for me. 1/2 my line is also blazed and panted long ago so that line is easy to follow. I just freshened it up this past summer actually. I add a bit of fresh flagging tape to the rest every year.