The front seal is in the timing cover. With the pulley removed you could dig out the old seal, but it's easier to remove the timing cover. Make sure that the pulley shaft doesn't have pits or is rough where the seal rubs. If it is, it will just eat the new seal. Better bearing suppliers have a sleeve, I think teflon, that slides over the shaft to form a new surface.
The rear seal is held in place by a 2 piece seal housing. The housing has a gasket
between it and the block. I believe the seal housing can be removed without removing the pan.
In this old post - Foley's rear main seal works for me. I have a 4108 generator engine