Autococker Pneumatics: Stock vs. Aftermarket
This is something of a marketing hype thing... simply because an aftermarket piece is available, everyone naturally assumes you MUST replace it or the gun will never achieve maximum performance.
#1) Rams are rams. There may be slight differences when you start getting into the HALO-fed 20+ BPS ranges, but for nearly everything else, any ram will do. Stock brass rams can be easily plated if that tacky non-chromed look isn't your thing.
#2) There's nothing at all wrong with a stock brass 3-way in good condition. The only benefit an aftermarket switch gives you- most of them anyway- is a marginally shorter throw, which allows for a shorter overall trigger pull. If you can stand having the pull half a millimeter longer than it potentially could be, save a few bucks and go with the stocker. They too can be plated if you'd like.
#3) The stock WGP reg is called a Sledgehammer. It has no easy external adjustment, and so is absurdly commonly replaced. The reg is decent, functional, durable and easily rebuilt. It can be adjusted, and fairly easily, but it does require somewhat more work to fine-tune than a Rock, Jack, Tickler or other aftermarket LP reg.
#4) The only difference in front blocks is 100% cosmetic. Stockers are blocky and square, aftermarket ones are milled, polished, annoed and smooth. But functionally identical.
#5) Center bolts (banjo bolts, front block screws) are center bolts. Again, the only difference is cosmetic- aftermarket ones are shiny, the stock one is dull and black. Plate the stocker when you do the ram and 3-way and no one will ever know the difference. Flow is irrelevant unless it's on a MiniCocker front block.
That being said, 3-ways are cheap. $5 each is all I'd offer. Rams are a little more, if it's newish and in good shape, $10 isn't unfair to anyone, though start at $5 or lower. Sledgehammers can barely be given away except as parts to the very few that use and maintain them. They should be extraordinarily grateful to get $1 for a near-new one. If they want more than that, I'd bet there's any number of Guilders that have two or three... I have a handful somewhere myself. (Did you know you can screw two together and have a double-regulated LPR?)
Front blocks might be worth a hair more, but I's still start at no more than $5. With screw.
Now, if there's an assembled, complete front assembly, with hoses and block screw, that's worth a bit more. $30 to $40 isn't unreasonable, even though that's roughly double the value of the parts seperately. Again, start low- $20- and work up from there.
It all depends on what you want. Looking to simply assemble a 'Cocker from scratch and on your own? I bet you could do it for under $200 of you get used parts and shop a little. (Shipping will add some if you pick up parts off of Classifieds or Ebay.)
Looking to build a truly top-of-the-line custom gun? Then you'll want newer or different components. But go the cheap way first, learn it, play with it, ruin a few parts (sear lugs, etc) fix it, then build another.