Easy to install and remove with a wrench. Contrary to modern pedals, mine (1980 vintage) had the flat part wide enough to allow the use of a standard wrench rather than an expensive pedal wrench. As for all pedals, the left one is left-threaded.
If they don't bulge, try to spray some nut looser around and wait 12-24 hours. And visit a bike- or car-mechanic that has a wrench of the proper size; don't use an adjustable wrench.
Mine worked trouble-free until 1998-1999. I had then to rebuild them a few times until they bit the dust in 2002 or 2003. So R.I.P after a little over 50 000 km, including some rain and snow.