Material Choice

I need to make a mounting adapter for the the ballscrew I plan to use on the Y axis of the Hurco mill.  On hand I have oodles (not quite a crap ton) of 6061, a little bit of MIC6, a little ATP 5, some 7075 (bought for a "special" project), and a decent amount of 4140HT not reserved for anything.
The 7075 would likely be the best of the aluminum alloys.  Its the strongest, but like I said.  I bought it for a "special" project.
The strongest by a lot would be the 4140HT, but it has its issues.  Its tough to machine, but I can do it.   It would have the least flex, or compression, but it can warp during machining.  I do have a toy surface grinder, but it has no coolant setup.  I have no desire to warp it even more trying it grind it flat after machining.
In between would be cast iron (very expensive) and mild steel (likely 1018) of which I have neither on hand suitable for this adapter.
For context, the adapter will bolt onto the location where the old ball nut was, and the new ball nut will bolt on to it.  It doesn't have to be absolutely perfect, but it does need to be "pretty good."
Ideas?  Suggestions?  Warnings?
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Bob La Londe
CNC Molds N Stuff
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