Scope instillation is not a hard thing to do, it's a small bit of dancing if you have never done it before especially in chosing the proper ring height and eye relief position. The simplest thing to do would be to have the shop install it with you watching the procedure and asking questions while it is done as that will put it into perspective the quickest---and not all shops provide the scope mounting service so it is a nice touch. Matter of fact, while there, ask if you can do the work yourself with their supervision/guidence lookin' over your shoulder-----this would help tremendously and most gunshop folks are quite helpfull.
The mounts and choice of ring height go hand in hand with the scope you sellect. The larger the objective end, more than likely the higher ring mount you will need. if you are going with a 28 or 32 mm objective, then more than likely the standard low rings offered from various makers will work depending on your barrel profile. The style of ring will depend on the style of base. If its a weaver base for example with the cross-slots, then the weaver rings, or leupold rifleman rings, burris zee rings, etc will function wiht that style base. Leupold dove tail bases require the turn in rings.
Your rear sight should be of the fold-down type on the mdl 39 so that should help as well to keep the scope off of it or out of the way. At 4x, you probably will not see the front sight thru the scope----you would see the front sight and front portion of barrel looking thru the scope if you had a 1x or 2x power scope as the field of view is so much larger.
To positon the scope, you want the cross hairs straight up and down in the rings. For eye relief, you will have the scope in the rings "semi-snug" where you can with minimal force, slide the scope forward or backwards to get the eye relief set for yourself. Have the occular end (eyepiece) too close to your eye or too far from your eye, you will not get a full sight picture wich will result in a half moon or three-quarter moon view thru the scope. Set the scope eye relief standing and holding the gun like you shoot---not on the bench--that way you are in your comortable shooting position that you would be in normally to use the scope. After you get your eye relief right and the cross hairs are straight, tighten her down.
I've used bore sighter tools before and they are handy for getting it on paper and nothing more. if you do not have a bore sighter tool, with the lever action your best bet is to eye-ball it on as straight as you can and with the 22, sight in close at 20 yards to get it where you want making adjustments and taking your time doing it, then back it out to 50 yds, and re-sight and make adjustments.
it will be trial and error the 1st time you do it but will be worth the learnin' curve especially later on should you decide to change scopes or get another rifle.
its kind of awkard at 1st just like breaking a gun down for the 1st time, but after you do it, it gets easier and easier.