Hey this may not be very usefull to Grifter folk but heres a way I use to get seized seat pins out.

Its for seat pins that have the saddle seperate on a clamp.

Well you oil them a day or so before commencing removal..oh I didnae tho..too  impatient.

Remove the seat and clamp from the end of the pin and the top of the frame.  
Ive got a bolt that is as thick as my thumb.  It fits in the top of the seat pin.  Well if the pin has a reduced diameter end I cut the very end off.  Then put the bolt in.  If its tight I either screw it in or hammer it in.  Then get the frame upside down.  Above the vice.  Place the end with the bolt in the vice.  Clamp it in real hard.  I put a scaffold poll on the vice handle to really get it nipped up firm.  Them try to move the frame side to side.  When I did my Burner the metal table was moving about.  Dont think this would work on a work mate then.

Most times when I do this I can reuse the seat pin.
I would have reffited the Burners pin but it was trashed by the other man.   Used it to clear out the seat tube though.  As there may be rust and muck or dents in there.

I know most Grifters have seats joined on to the pin.  But there are some Grifters that have removable seats.  Also if your using a Shopper bike seat pin.  They fit Grifters and are quite long.