Building an effective refinery ship from a small welder array using merge block

I have already built an effective large grid torpedo welder. The torpedoes are 2X2X7 blocks long. I want to build a refinery/assembler ship from the same welder array that I use for the torpedoes, but to do that the blueprint needs to be way longer than 7 blocks. To overcome this problem I want to weld up 7 block long sections of the ship at a time and then use merge blocks to eventually bring the sections together into one ship; completely automated.

I would like to be able to weld up the...

Building an effective refinery ship from a small welder array using merge block