If the bike is old enough to have a 5 arm 110 bcd crankset and a 13 or 12t top gear it probably came with like a 36 or 38 middle ring. If it’s a 4 arm 104bcd it’s likely a 32 or 34.

If you keep the existing crankset, the ring mounts on the middle position and it’s a little thicker so you might drop a size from the triple middle max clearance. But there might also be tons of clearance. I put a 48-38-28 on my 2002 Hotrock no problem even though it was from the 42-32-22 sort of era. You might also get some more dialing in the chain line with a longer BB because the best for 1x is a little right of the triple middle.

It might do more than it has to begin with but don’t count on it without checking.