The best thing you can do for yourself especially if you live in California is buy pre 1975 because it's smog exempt and you know what a pain in the ass it is getting a vehicle smogged so you'll never have to worry about it again and current registration if it doesn't have current registration when you start the project make it current you don't want to have to deal with registration problems after you've already put a ton of money into your project vehicle
Salvage title does not mean stolen. Insurance companies place salvage titles on vehicles that have been crashed, stolen and recovered, flood damage etc. if they determine that repairing it is not cost effective then they salvage it. Many owners opt to buy it back from an insurance company and then repair it themselves. It is true that a vehicle is devalued when it has a salvage title but if you are planning on a frame up build, possibly even replacing most of the frame then it may be a better value to purchase a salvaged title at a reduced cost to enhance your build budget. Depends on how quick you plan on selling it after you finish your build. In other words if you plan on keeping it for the useful life of the build then don't be afraid of a salvaged title. Just do your homework on why the vehicle received a salvaged title in the first place.