There's a bit more than that. You'll want to add some extra code to the URL to make it show all the posts, or the post numbers won't read properly.
Use This Template:
https://rpol.net/display.cgi?gi=[GI]&ti=[TI]&show=all#[PN]
Where [GI] is the game number, [TI] is the thread number, and [PN] is the post number. If you are looking at the thread you want to link, you can find the GI and TI just by looking at the URL.
Just replace the parts in brackets with the right numbers (removing the brackets, of course).