This chart will give you an idea of my height rings you need for your scope.
http://www.midwayusa.com/midwayusa/staticpages/charts/ring_height.htmAt a minimum you will need medium scope rings depending on your scope. The diameter is the exterior measurement of the objective bell. I recently bought a new set of rings, but before doing so I measure the objective bell of the scope with my calipers. The set of calipers I have measurers in millimeters and inches. Have to admit it was the first time.
This is the base I have been using for close to forty years on my 336. Using this base I have had no issue with the rear sight.
http://www.midwayusa.com/viewProduct/?productNumber=189486I looked all over the Weaver WebPages and could not find adjustable bases, just rings.
http://www.weaveroptics.com/rings_bases/rings/detachable_alum/suregrip_windageadj.aspxI like the idea of adjustable rings.
Normally I am on the same page with
cwlongshot but I have to disagree this time. A scope with a 42MM Objective lens will require a medium high base on your Marlin when you add in the bell housing diameter to the lens. You want a little clearance between the scope and the barrel, including the rear sight. I do go for the lowest mount giving me the clearance.
I had to go to medium rings on my 336 when I installed a new scope on it. The objective Bell was not the issue, but the large eye box on the scope. I needed the clearance for the hammer. Suggest you check that out.
As you can see the hammer just clears the eye box on my rifle. The problem was when the hammer was cocked it would jam against the scope. If you are mounting your scope way forward of that position, the scope should be 3-4 inches from the eye you are pushing the scope beyond the eye relief distance it is designed.