OP, sounds like what you really need and want is a hybrid. Just go buy one and be done with it.

If you choose to mod the old bike, convert to a threadless one inch headset and buy a CF fork or new steel fork and leave the tube untrimmed and stack it up with spacers. Once dialed in do the final trim. Much better selection of stems for these types and one inch threadless are still out there for new purchase.

Me, I am 65, never quit riding or swimming or running or lifting, I prefer my old steel racers and am fine with them As of late have an infatuation with aluminum tripe triangle GTs. I would not hesitate to purchase a new bicycle if I wanted one but I hate disc brakes and am not fond of CF and refuse to ride a "me too" Specialized, Trek or Cannondale. I go to a ride or a race event, I swear, 97% of the bicycles are one of those three brands. Give me a brake, a rim brake that is.