Congratulation on your deal.
It is a lovely bike.
I got myself recently a 1995 De rosa Giro d'italia in almost perfect condition for 200€.
It came to me immediately the same old question. Stolen or not. ???
I could have refused the deal, but someone else would have picked the bike.
I informed the seller that it could sell it for more money, but it was okay for him to sell it at this price because it pay the same price for it from a friend, just to try if he could enjoy road bike . this bike was clearly too big for the seller, so he decided to sell it and purchase a nice bike with the right dimension.
After that, I told him that I will take the bike only if I could pick it up in person at his adress, (just in case I may had trouble in the future). No problem for him, very nice guy I must say.
Finally, I shared pictures of my purchase in forums (in france). If someone recognize his bike and can prove without any doubt it is stolen, of course it will be given back without any problem.
I think sharing pictures in such case is the best way to prove that you are honest.
We can find everyday good opportunities if we are good looking at what is available.
A lot of people ignore totally what they are selling.