Is it safe (damage wise) to use an aluminum DIAS in a Sendra lower that the "pocket" in the receiver is milled out like an M16 VS a Colt AR-15 that is narrower in that area (so a GI sear cannot be installed)

I have both rifles but have been reluctant to install a very expensive DIAS in the Sendra as it appears to have less "support"  in that area.

Anyone have good or bad experience with this?

THX fer lookin

You could reinforce the aluminum dias body against the takedown pin post in some manner. It's not a high stress area, but allowing it to flop or flap is never a good thing.

Anything from a rubber band around the body, to a custom clamp or 3d printed custom plastic shell might be useful to help secure it.

As long as it is a RDIAS, that will be fine.
However, if you you are getting inconsistent sear tripping, you can use some shims made from feeler gauges to get the correct thickness and place on the bottom/back of the RDIAS so that the upper takedown post secures the RDIAS firmly for correct timing. I have done that with a couple of uppers that didn't quite fit right. I used black RTV to glue the shims in place after cleaning everything with acetone.

Why risk any issues?  Just buy a new low-shelf lower to host your RDIAS.  ~$100 to get a new stripped lower seems like a no-brainer.

Agreed!  Get a new lower. Option up to a nice properly marked one, maybe even ambi lower, you have options.

Agreed-ed

DIAS indexes to the takedown lug, the milled pocket offers nothing.

If your DIAS is not snug around the takedown lug, you need to fix that. Relying on the pocket (SP1 or otherwise), to keep it from moving around is a mistake.

Thank you, that is the answer I was looking for!

I would agree with Renegade that a DIAS indexes fore and aft in the receiver off the rear takedown lug.

However, the pin that holds the trip is also held in place by the right side wall of the receiver which is thicker to preclude a standard M16 autosear from being installed.

If you install a RDIAS into a M16 sear milled pocket there is going to be a decent gap between the right outside wall of the RDIAS and the right interior wall of the receiver. (plus a smaller gap between the left wall of the receiver and the left body of the RDIAS.

This gap could potentially allow the RDIAS trip pin to walk laterally in the RDIAS body.

Now many RDIAS have the pin quasi staked or press fit so it can't walk out of the pin holes.  It also may be that the gap between the right outside wall of the RDIAS and the right inside wall of the receiver is small enough that the pin can't laterally walk to the right enough that it could lead to the left side of the trip pin to come out of the left wall of the RDIAS depending upon the DIAS body left wall thickness.

However if that sear trip pin did walk to the right and the left side of the pin clears the pin hole on the left side of the DIAS body its going to probably damage the right DIAS pin hole in short order having the pin unsupported on the left side.

Not saying you can't use it in the Sendra receiver but I would check to make sure that pin can't potentially walk laterally to the point it could become unsupported (especially on the left side)  of the RDIAS body.