Bear with me as I don't know what you've tested, or not.

First, make sure the hammer/trigger pins can actually go through the holes in the trigger pack and receiver separately.
If so, one or the other may be out of spec, or, you may have run into tolerance stack, where one part is at max and the other at min tolerance.

If you have a set of dial calipers, measure the distance from far edge to far edge of the holes on the trigger and receiver, then subtract .156 for the center to center distance.

Your measurements should be very close to .900" +/- .001"

The math works out like this:

Solve for Hypotenuse of Triangle with
A horizontal distance CtoC Hammer/Trigger pin hole = .843
B vertical distance height difference of holes = .314
C Hypotenuse X
Standard formula A².710649 +B².098596 = C².809245
√.809245 =.899580

Let us know the results!

trigger "fits" but it won't fit down in the well. I'm going to take it to work on Monday and try it in another couple of lowers but I suspect that the interior of the Delton lower is a shade not deep enough and further than the bottom is a bit asymmetrical, right and left and not quite as deep on the left as on the right. No, I didn't measure, just ran out of time and put the original trigger back in so that the firearm would be functional. Might get a new lower but not excited about that. Might get one of the really inexpensive ARs and see if it will go in one of those. Our gunsmith has installed many of these triggers and this is the first instance of this he's seen.

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Sincerely,

Hobie