Look mate i wana kno y you need to remove it for starters because personally i have no expierence with skyline flywheels but a dowl on the crank is usually to dummy proof install of a fly wheel for timing reasons in some vehicles im not sure on nissans tho also if its completely necessaey to take it off without touching the crank cut it off then drill it out only so far in as its sticking out, start small n work ur way up untill u can use a small flatty to pick the remainder out use a chizel effect if u kno what i mean
Hope this helps!