I've found many greedy sellers, in Italy, with prices 'till 18.000 euros

A few days ago I've lost a wonderful black first serie gone away for about 5.500, and now I've found a 1980 for 4.500, 64.000 km (less than 40.000 miles)
I've made searches in this forum and on the Net, seems to be an affordable bike, but there is some thing I have to pay special attention for?
Engine? Chassis?
Some pro link are now available for about 6.500-8.000 euros, I know they has some not better known 'chassis improvements'.
I would to install 17 inches rims, modern fork and brakes and rear suspesion from Fazer or other fittable, the loss of power from the first series is not a problem: should I prefere a prolink for this transformation and every day use?
Note: I can do myself many works on it.