Firstly, if that plunger rebuild kit is still available on flea-bay then buy it, its cheap. I'll explain why in a minute.
First thing you need to do is work out exactly what is stuck as there are a couple of possibilities. With the pinch bolts top and bottom and the bolt through the lug done up can you twist the lug, if not then you know for sure the centre tube has seized on the shaft. If you can twist it then the next most likely cause is the spacers (part no's. 5 and 14) have rusted to the shaft. If this is the case you will be able to twist things but the shaft will not come out.
If the spacers have rusted up then a few days with penetrating oil and a smack with a hammer every now and then will free them. If you have a lathe or a friend who can do it get a old piece of tube and thread it to screw into the top of the plunger shaft so you can clobber it. By the way, the plugs that are in the very bottom of the shafts are just plugs, they come out. If you put a piece of rod down through the shaft they will knock out the bottom.
Now if the centre tubes have rusted to the shaft things get a bit harder. There are a couple of ways around this. First remove the grease nipple and use a piece of wire or a small screwdriver to dig out the old grease and try and get as much penetrating oil into this hole as possible. This is the only way you will get oil to the rusted bushes. If the grease inside has gone hard then this wont work. If all else fails then there are two ways to get them apart.
First method is to drill the shaft out from the top and bottom. Second method is to get two small wedges of wood and jam between the top cover and the frame, you only need a gap the width of a hacksaw blade. Then cut through the shaft with a hacksaw. Do this to the top and the bottom.
You will need new shafts and bushes in the centre tube and quite likely new springs as these are usually compressed and not the same length.
I recently had a pair of shafts hard chromed and ground and it cost me AUS $260 and then I had to make the bushes, thats why those ones on flea-bay are cheap.
Have fun........................