Ultimately the only thing which will define your collector will be the packaging requirements. 6-3 3-2 2-1 would make for a nice shallow merge, but that don't mean ---- if you can't get it to fit.

 

but can you make it fit just like a 4-1 if you jigged them at the right angle? yep. Plus, you can push 4 of the round edges in some and pull the side edges out to make it a rectangle, any bit of creativity can solve the alignment problems, even 4-1's still have some over/underhang.

 

my 4-1 has no overhang.

Not sure how well this works with 6-1 but for a 4-1 you just make a circle and weld just two halves. A large belt sander will take care of the rest. Here's what I mean.









I cant see why this wouldn't work on a 6-1.. would be more work though.