After i had cut out the new piece of plastic (cut out on a scroll saw then trimmed up with my dremel and a sanding bit) i drilled out the post holes, i then used a tapered bit in the Dremel to taper out the tops of the holes (didnt get a pic of this step) so i could bend the tops of the posts to grip into the plastic (peen them over) I wasnt quite sure how i would do this, first i used a drill bit and a hammer to push the taper back out to grip the plastic which worked but looked a little rough. In the end i used long nosed pliers as shown in the 1st pic, twisting them inside the metal post to hopefully push the metal out a bit, it seemed to work pretty well. This step isnt really necessary as once they are screwed down they wont go anywhere 

2nd pic the finished plastic after the edges had been sanded and polished, started with 80 grit sandpaper, then 180, 280, and finally 800grit wet&dry and Windex, followed by a polish with Novus to finish them off.

3rd pic , the guide installed on the pf

last pic... i decided to do the righthand side one as well  

i had already polished up and fitted the righthand side one as it wasnt broken, but was all yellowed and crappy looking compared to the newly remade left side one