Re:
That's a nice-looking frame, designed for touring (fittings for a rack and mudguards at the rear). 27.2 a common seatpost size but the tolerances and differences are small and some trial and error with seatposts sometimes unavoidable. The decal suggests round about 1990, but decals can be applied later on and it may have been built earlier.
753 was designed to be about as lightweight as steel got at the time. You may hear some stories about giving a harsh ride, not being suitable for touring, being fragile, etc, but wouldn't take much notice of these. I have a lot of steel bikes and 753 is my favourite ride, fast, comfortable, responsive, even on the harsh road surfaces in the Dales, Howardian Hills and the Wolds surrounding York. I haven't toured with this one but have seen a number of cycle tourists on 753 bikes over the years (not too many, these are uncommon tourers!) and they all swear by them. Still get people asking if they can pick the bike up outside cafes to check on the weight, these are generally well-built and cherished frames.
Suspect the only slight complication will be around wheels and numbers of gears you can get but there's already been some sensible advice about what to do. All I would say is that mine originally had 6 speed at the back but I ride 10 speed and haven't had any problems (built up with Shimano Ultegra components, Cinelli stem and bars and a Campag seatpost with a Brooks saddle).
This is a frame to be built up and enjoyed.
Good luck.
