I have taken care of my telescopic sight need - Burris Euro Diamond 1-4x24 mm (30 mm basis tube). Mounting on my rifles - that's rifles, plural - needs to be addressed.
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Results wanted:

- Low rings for 30 mm basis scope tube that can be detached from mount and re-attached without disturbing zero. These need not be quick detachable - just detachable.

- Mount for Marlin 1895s to use rings sets identified above, that incorporate some sort of pop-up/retractable aperture sight. If this is not available in a mount-rings assembly that places scope low enough over centerline of bore, is there a side-receiver-mounted aperture sight whose stem can be detached from mount and re-attached without disturbing zero? I thought Marble's tang sight was my answer, but shooting my heavy 45-70 loads caused Marble's pivoting knob [for stem] to punch me in the nose. Marble's sight is a perfect solution for right-handed shooters; I am left-handed.

- Mount to be available for bolt action receivers also. My intention is to be able to mount the sight on any of my rifles, adjusting zero as necessary. As I write, however, my metallic cartridge hunting rifles are 1895s.

- I strongly prefer mount-rings assemblies to not be made of aluminum.
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Help me out here?

I don't know of anyone that offers what your looking for in steel. But this base would fit the bill other than being aluminum.
XS Base

For the rings I have used the leupold quick detach with great success. I have them on a browning Blr for my scout scope. The base is aluminum and it was held up fine to recoil of 358 win and the steel rings have not marred the base in anyway.
Leupold QD