MPN: SP-5002 will work well with your Tikka T3x TAC A1.
The Spuhr 35mm Rifle Scope Mounts are offered with a centerline height of 1.5" (MPN:SP-5002-DEMO/MPN:SP-5002/MPN:SP-5602), a 1.3" height (MPN:SP-5006), and 1.18" height (MPN:SP-5001-DEMO/MPN:SP-5001/MPN:SP-5601).
Because you intend to mount your scope to the MR762, which is very similar to the AR platform, you would need to use a higher height mount regardless of your objective lens in order to provide a comfortable and more usable head position. The 38mm height Spuhr 35mm Rifle Scope Mounts would be my recommendation as they will provide enough clearance for your objective lens and allow you to have a comfortable head position. The 0 MOA model should be just fine unless you are planning on shooting targets past 600 yards on a regular basis. For further assistance, feel free to email us at Techsales@opticsplanet.com.
For that set up I recommend using the Spuhr 35mm Rifle Scope Mount 38mm high model. The 34mm high model may work but without being able to measure it I recommend the 38mm model to ensure enough clearance.
The Spuhr 35mm Rifle Scope Mount you need will depend on the scope you are using with that rifle. If the Impact Action you are using has an integrated picatinny scope base the Spuhr 35mm Rifle Scope Mounts will mount to it. The guide at the link below will help you determine what height you need for the specific scope you are using.
https://www.opticsplanet.com/howto/how-to-how-to-measure-scope-height-scope-ring-height.html
The correct ring height you need in the Spuhr 35mm Rifle Scope Mounts will depend on the scope you are mounting to an AR15. The guide at the link below may help determine what ring height you need.
https://www.opticsplanet.com/howto/how-to-how-to-measure-scope-height-scope-ring-height.html
To mount that scope on a SCAR 20S I recommend using the 38mm high Spuhr 35mm Rifle Scope Mounts. There is a 0MOA and 20MOA 38mm high Spuhr 35mm Rifle Scope Mount, so one of those two models will work.
For that set up I recommend using the 30mm high Spuhr 35mm Rifle Scope Mounts. You should have enough clearance for the objective lens using the 30mm high mount on those rifles.
I would use the 38mm or 34mm high Spuhr 35mm Riflescope Mounts to ensure enough clearance.
The Spuhr 35mm Riflescope Mount that I would recommend to you is the 38mm mount with 0MOA (MPN:SP-5002) or 20.6MOA (MPN:SP-5602). If you are planning on consistently trying to hit targets 600 yards and further then it may be more beneficial to you to have the 20.6MOA mount, due to the extra elevation adjustment it will give you.