Icengineworks offers 4-1 collector dummies that would be perfect for formed collectors. However, I have fabricated double-slip collectors that have slightly wider on-center tube spacing. In addition, the 180-crossunder design requires that both sides are mocked at the same time. This necessitates two dummies at a cost of $199.99.
So I decided to design and 3D print eight female adapters. These provide the perfect spacing, were printed faster than over night shipping and cost less than ground shipping for the other pieces.
Merge collector with female adapters installed (the double-slip fittings aren’t shown), 2.0” OD block with the male end up (yellow), front side of the female adapter and back side of the female adapter.