Although the question was not asked from me but still I will answer it.
Dont go for overhaul you will get the complete engine alongwith head, block assembly, throttle, coils and every sensor new in 20k plus your engine.
L12 is 1248 cc
L13 is 1332 cc
But you wont feel any real difference in ride quality in daily drive but yes on motorway L13 easily climbs salt range in 3rd & 4th with fully loaded car and yes another thing is that L13 is more fuel efficient than L12 I dont know why