I had the top tube and down tube replaced on my road machine some years ago and regardless of how good the framebuilder is, reheating the joints causes the lugs to become brittle( a metallurgist or engineer will tell you it is to do with the grain structure of the steel) and whilst it should be fine for a few years, it is likely to fail after a few years. Mine went on the lug joining the down tube to the head tube just after I had been descending from the top of the Malverns and, thankfully, I was given some pre warning that something was amiss i.e. the bike started to flex a lot!!!
Should remember too that, because the original forks will have been wrecked, you will have to replace those too - lets say another £50. Also as it is a Lo Pro, are they 700C, 650C or 24"? So by the time you have bought a dodgy frame for £500, replaced the tubes for £200, resprayed(minus chromium plating) for £100 and bought a matching pair of forks for £50 you have a total of £850.
Not sure if you are interested in the frame for the Colnago name or for the geometry of the frame i.e. sloping top tube and curved seat tube, but alternatively you could:-
Buy an interesting British built frame from the 80's or 90's which has usually been built by the guy who has got his name on the down tube and who has, most probably, built it with the required skill and lavished it with due care and attention during the build;
Go on a frame building course for a week and come away with your own tailor made machine.
I would suggest either of the above is much better than splashing out lot of money for a repaired frame. Sorry if I am missing something but those are my thoughts and I hope this helps.
Or just go to the sale thread and look at Hilary's name-dropper-friendly Lo-Pro bargains.
Or just go to the sale thread and look at Hilary's name-dropper-friendly Lo-Pro bargains.