I assume you want to use parts of one forge, and parts of another to give the look of one made of differing colors?
The only real way is to get the first one placed, break it, and chop away the pieces that you do not want. The use a castle-ladder to place a series of goza mats way above the original pieces and place the 2nd soulforge on that. Break it, lower the pieces a little, remove the goza-mats, chop away the pieces that you do not want, and lower the remaining pieces to the level of the original soulforge.
It's rather complicated, but should work. To do it, you'll need the soulforge in an area that has no roof, or at least a room with 2 stories in height.
Good Luck!
