The UCA hitting the mount is a common problem with the tubular UCA's that have a tight "V" shape. The stock mount just wasn't intended to accommodate the tubular UCA with that kind of angle. The only way around this is to have a UCA with either a "U" shape, or a partial "V" shape with straight legs at the ends. There's more to consider too, because the "U" shaped arms will interfere with the rims and turning radius if you start mounting significantly wider tires up front.
You can cut the UCA mount back without sacrificing the structural integrity of the mount if you do it right. This is a much easier problem to deal with than the other issue you've got. The upper part of the tab doesn't do much if anything for strength. Leave as much of the corner as you can, because that does add strength, and only take the cut down as far as you need.
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If you don't want to make that relief cut, you'll have to choose a UCA with a more rounded shape.
These are the CPP arms. Anything that looks like this will need that relief cut made
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Like these non-adjustable arms from PST. You'd have the same issue with needing to clearance the mount. Magnumforce makes non-adjustable arms just like this as well, same issue with cutting the mount back a little.
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Here's a QA1 arm. This one should clear, you can see the difference I'm talking about in the legs of the UCA with one having a bend in it
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UCA's from Firm Feel. Notice there's a straight section on both legs of the UCA. Shouldn't require any modification
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Same with the Hotchkis arms, although these have heim joints which I'm not a fan of for street cars.
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These are PST's adjustable arms. Notice the
really wide shape. I would bet that I'd hit these when turning the 18x9" rims I have up front. And heim joints again.
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