Originally Posted by Carbonfiberboy

Yes, correct. From competitivecyclist?

Because of the small frame, I don't think you'll be able to exactly duplicate your current bar height using a threadless adapter and modern stem. But that's the path forward. I think you'll like the new position a lot once you get used to it. Two hours doesn't seem like a long ride if one's position is right. And you'll vastly prefer riding on the modern brake levers' hoods.

The alternative is to start with a new, larger frame, an endurance frame as mentioned by another commenter. The forks on new bikes arrive at the shop with long steer tubes on their forks. The steer tubes are cut to length for the buyer's fit. Thus you can get your stem up higher with a new bike than by using an adapter on your present bike. I regard your current setup as very unsafe. I might rip that stem right out of the bike on a hard sprint and it could also fail under emergency braking or hitting an unseen bump on a descent. The physics are not good. Having one's front end come apart during a descent is not good.