Bought a Vintage Bianchi 1985 road racer, came with Shimano 600, can I easily turn it into index shifting?
Some pictures of the levers and the RD may be welcome and clarify the situation.

Shimano 600 was an indexed shifting system and stands at the beginning of the Ultegra line of products. It can be switched from friction to index by turning the toggle at the side of the right down-tube lever (if you have the original Shimano 600 levers). However if you have standard friction levers you'll have to find a pair of original 2x6 levers. Although the 2x6 thing bothers me a bit as the 1980s Shimano 600 tri-color that I own is 2x8 and cassette type instead of freewheel. It suggests that there are some non-original bits in your recent acquisition. Pictures please! 

Indexing happens in the command levers, there is no such thing as an indexed rear derailleur. So there is no need for acquiring a different RD if it is indeed a 600.