Is it the original seatpost? The one on this 1984 catalog photo looks like it may already be raised close to its maximum useable height. Older stems were commonly made with a shaft length of only 180 to 200 mm and for 4" to 5" showing above the seatlug and 2-1/2" below the limit line - which allowed for what was considered a normal bike fit for that era.

Just buy another post. New posts are commonly made to fit modern mini-frames, so they're often available anywhere from 300 to 400 mm long (4" to 8" longer).

Could be worse... I have some top end racing bike posts from the 1960s with shafts only 130-150 mm long!