For this set up we would recommend the UltraMount in a 1.54" height.
The height measurement of the mount is from the top of the picatinny rail to the split in the ring. I don't know the EO Tech dimensions so I can't make a recommendation but you should be able to calculate it with the height measurement.
Yes the 34mm 1.5" will work great.
We would recommend 1" in height unless the chassis has a handguard over the top of the barrel then you will need to go higher.
Our recommendation would be the A496 1.5" Ultramount 0MOA. or the A699 1.54" Ultramount 0MOA
That scope and mount combination would be an excellent pairing with the SCAR 20S. The main benefit of the Magmount on that particular rifle is that you can orient the cross-bolts away from the charging handle, so they don't get in the way when charging the rifle. You could also use the A361 1.5" 0 MOA Magmount. Either of those mounts would be ideal for your SCAR.
On a traditional rifle like the Tikka, the Magmount will likely be too high without a cheek piece it will be difficult to get a consistent cheek weld. I would recommend a set of traditional rings such as our A101 30mm medium ring. this will place your optic almost a half inch lower than the lowest Magmount.
I would recommend either the A162, A361 or A362. I might also suggest a set of rings at a height of 1.125". As with all mounting hardware these are just my suggestions, there may be factors I don’t know about and there are many other ways to mount this optic to your rifle. I highly recommend mock mounting everything first in case there is something about the set up you wish to change. If you have any other questions please let us know.
The A362 Magmount would work well for the ATACR 7-35x56. Just be aware that the Barrett MRAD often has MOA built into the integrated rail so you may be doubling up on your taper.
Many of our mounts would work well for this rifle. The ideal mounting solution would depend on your optic as well as your intended use for the weapon. Also check out our X-Treme Duty – Ultralite Rings.