The M14/M1A is just a hoot to shoot and, while adding an optic is somewhat problematic, doing so is not impossible. In my experience, the greatest problem you will have is achieving and maintaining a consistent and repeatable head position which is paramount for consistent zero and precision.
The best alternative I have found for accomplishing these goals are to put the barreled receiver in a Sage ALCS Stock and mount the scope in a Sadlak Scope mount. If the Sage ALCS is too pricey for your budget, the Bradley Cheekpiece others have recommended should go a long way to helping to achieve a consistent and repeatable head position. Unless you can find an original Brookfield Precision Scope Mount, the Sadlak is best choice. If you do decide to put your barreled receiver in a Sage ALCS, DO NOT LET THEM TALK YOU INTO USING THEIR M14DCSB! (DCSB: Dual Cantilevered Scope Base)