I've never used them. Nova Cycles Supply is another resource for framebuilding supplies. As far as the seatstays and the dropouts, the seatstays are tapered. You can cut off the small end until it fits nicely in the dropout. You also need to take into account what type of filler material you are going to use. Silver needs a close fit up. Brass needs a bit more of a gap for the filler to flow into the joint.

You will find that none of this stuff is just plug and play. It will take some massaging of the metal to make things fit together.