Welcome. A quick use of the board’s search function (upper right of the page) for “2454” indicates that it was marketed as a 6/7, which BTW is a pretty good default for 8’ vintage glass. Since you’re new to fly fishing, and assuming you don’t have a variety of lines handy, I’d first try to borrow a 6 or 7 weight line on a reel from someone, give it a cast and see what you think: if it seems to labor getting a cast out, first try a shorter cast, then a lower weight line; if if you think you’re really having to power and speed up your cast, try heavier.

Usually when someone picks up an old, and unknown to them, rod there’s a certain amount of fun trying it with a few different lines; modern lines are different than what was available decades past, and individual preferences vary, but that can be a little tough on the first-timer. But glass rods usually handle a decent range of lines, at least adequately for fun fishing, so don’t worry too much about dialing it in.

Have fun.