The offset looks pretty right. My motor is out & all in bits so I can't say what the actual measurements are, but the top front engine mounts on the frame are 59mm apart & centrally spaced between the down tubes, while the bottom ones are offset approx 5mm from central to the left viewed like your photo(20mm to side rail on left, 30mm to side rail on the right. Now I'm confused!!
Hope this makes sense.