Typically, with an objective lens of 40-42mm, you would use a low height mount. It can vary depending on what rifle you intend to mount your scope to, but either way I'd still recommend the low height.
Using the Sig Sauer Buckmasters 3-9x40mm Rifle Scope on an AR15, I would recommend using the high height Stainless Steel Hunting Rifle Scope Rings (1" tube). MPN:SOA10008
On the AR15 platform, you want to have a high height mount to allow for a comfortable head position while shooting. There are scope mounts specifically designed for the AR15 platform that I would recommend over standard scope rings. You can find a 1" scope mount that I recommend using the following link:
https://www.opticsplanet.com/primary-arms-primary-arms-deluxe-extended-ar15-scope-mount-30mm.html?_iv_tube-diameter=1-in&_iv_additional-features=standard
Sig Sauer does not state the exact width of the crossbar on the SIG SAUER Alpha Stainless Steel Hunting Rifle Scope Rings. However, they are stated as being compatible with Picatinny Rail but not Weaver Rail.
Medium height rings can support Objective Lens sizes 40-49mm. Typically high mount rings are better suited for objective lens 50mm and larger.
The Sig Sauer Whiskey3 4-12x40mm Rifle Scope uses a 1" tube, and you would need rings that accommodate 1" tubes. As for the height, it can depend on the rifle you intend to put to scope on. For the AR15 platform, I'd recommend the highest rings available. For a bolt gun, or 10/22, anything else, I'd recommend low to mid height rings. You can find out more about the height you would need by using this how to guide linked below:
https://www.opticsplanet.com/howto/how-to-how-to-measure-scope-height-scope-ring-height.html
The Sig Sauer Alpha Stainless Steel Hunting Rifle Scope Rings that I would recommend for the Optika5 4-20x50mm Rifle Scope on your rifle is 1" tube, with .98" in height. MPN:SOA10008. You can find out more about selecting the correct height rings by using this how to guide linked below:
https://www.opticsplanet.com/howto/how-to-how-to-measure-scope-height-scope-ring-height.html
Yes, these will work on your Marlin.
Yes, these would work, assuming you already have a picatinny rail installed? You could go with the low or medium height:
SD9-RR-SATRR-SOA10006
If you need a rail, email us at techsales@opticsplanet.com and we will help you find the correct on for your rifle.
For a 42mm objective lens you will want to go with the Medium Height rings (0.38")
For a scope with a 50mm objective lens you will need High height rings (0.98")