I almost purschased a mint condition green 77 911s with 80,000 miles.
Top end rebuilt at 52,000
Brakes overhauled.
Paint in very good condtion and interior near perfect along with all rubber seals. Won a few awards at Porsche shoe's in the North East.
All motor Upgrades were performed but the owner left the Thermal Reactors attached
He would not go lower then 12k and it's still for sale
So I picked up an 82SC Targa for a bit more $$ but well worth it.
2.7's are a decent motor as long as they have been rebuilt correctly and the 77's had the updated valve guide material.
I've noticed that the going market price is about 10 - 12k for a realy nice one max for now.
74's are not galvanized but they did not have the smog devices attached and seem hold a higher value on the west coast.
Mid Year models are not that bad but they are stuck woth the 2.7 problem stigma which makes them harder to sell sometimes.
Make sure to have a thourough PPI performed.