Will order a CPA bench rifle in 32-40 this week . Have no interest in external adjustable scopes . I know from past experience with my 1885 Low Wall that I needed a scope with a rather long tube length to extend far enough back to be viewed . Short scopes just will not work on this rifle . If I purchase a Weaver T-36 scope for my CPA will the scope have enough length to reach the eye to make it comfortable to shoot or are modern scopes all to short for the single actions ?

I'm using a Weaver T36 on my CPA with no problems.  The scope blocks need to be mounted close to the action to get the correct eye relief.

JS

Night Force 12X42 BR plenty of eye relief. Returning back to my roots, external adj. traditional optics and sand bag front rest.

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Steve Earle also produces various "rails" that let you move modern target scopes with short eye relief back over the action.  Brownells sells various types of scope base stock by the length that can be adapted as well. 
One thing I have found with extending a sight rail back over the action of a single shot is that it does not leave a lot of room for access to the action and that sharp corners on the rear bottom of the rail have to be radiused for your fingers sake. 
I have the smallest FBW (which has high sides like a hi-wall) action in .17 Mach IV/ 17 Fireball with a modern varmint/variable scope that is cantilevered back over the action; and getting that little cartridge into the chamber can be a PITA and in the fingertips too. 

Brudford, Keep in mind, if you use a base that extends over the action, you'll have to remove it before you can unscrew the barrel.        ...MIKE...