820 on are all cromo main frames-sometimes 800 also
I buy/sell lots of Treks-700,720(700c wheels),800,820,920,930,950 etc. Most have main frames of all cromo.Some of the 700's and 800's have just the seat tube made of cromo,and the rest is cheaper steel.The earlier 800's have main frames of all cromo.The higher the # the better the frame-the 920,930,950 are all cromo and all double butted-usually True Temper OX II-many made in USA,later ones made overseas.
Your new bike is very nice.Fixed up as it is it would sell for $125+ around here(New Orleans)-more in other markets.It looks big-20" or so?
Luck,(but you don't need it),