How does one go about removing simplex crank arms, I have a 70's model Peugot... I removed the small bolts on the underside of the crank arms near the spindle. Also, there is a plastic piece in the area where one would normally use a crank-arm puller... which I cannot seem to remove...

Any advice... I would ultimatly like to use these cranks again, so I don't want to damage them...

Any advice would be much appreciated.

Thank you.

Those sound like cottered cranks. You can either buy a expensive tool to remove the pins, or tap them out with a hammer. The crankarm will fall off when they are removed.

Also, if you've got a used pedal spindle laying around, that'll fit into the hole perfectly in case you break the bolt with the hammer, or bend it and have to cut it off flush. Just hold it on there like a chisel and whack it.

Here you go, sir.
https://sheldonbrown.com/cotters.html