I have a great candidate barrel to do a 605 build.  It is an M VP 12 that was cut down to 16".  My question is what components would be correct for a build with this era barrel? I have some parts that I could use to build it, but Retro Black Rifle does not go nearly into enough detail for me to know if they are correct.  It would seem that I need a partial fence lower set up exactly as would have been found on an XM16E1, with my choice of dimpled or non-dimpled pins depending on how early/late.  When was the 605 produced and where in production would this barrel fall (I assume later production 605)? Same question goes for which would be the proper upper, a regular slickside upper or do I need to get one of the uppers with the weird bump where the forward assist should be? If using a regular slickside, should it be square or round forge? Chrome or parked carrier and with or without forward assist serrations? Thanks for any help you guys might be able to provide.

Your barrel would be perfect for a 605, but to be correct it should be 15". John Thomas can cut, re-thread and permanently attach a 3 prong and shave the bayo lug. Partial fence is correct, slick upper will work fine for most but the upper with the ground off FA boss is the ultimate feature that the 605 is known for. NDS used to make them, real ones are very hard to find. 1964-65 is the era iirc. B,C or D stock, edgewater buffer, 601 style extension (tube), chrome slick BCG, either dimpled or no dimpled pins will do.

Here is my cloned 605. NDS upper/lower. Fulton Armory chrome slick side BCG. USGI Colt 15" barrel (was 16" when I bought it) that John Thomas trimmed and pinned flash hider. Type D stock, original handguards. Great reliable rifle that gets the look when ever I go to the range. It works just fine, even in the rain. Since this picture was taken I had JT dimple the take down pins and safety, and magazine release.