200 disco engine - crank pulley

Hi
I'm trying to put a disco engine in my 90 and need to replace the crank oil seal but I cant get the crank pulley off. A normal 3 legged puller wont fit so I assume a special puller is needed which I cant find any referance to. I have tried all the usual things of heat and levers but if I use any more force I am sure to break the aluminium casing! Can any one help?
Phil

i take it you've undone the single large and 4 10mm smaller bolts ?

a very slim drift down the back usually works for me, work it around tapping gently