Been a long time since I looked at a 4.108 but if I recall
the pump is bolts onto a flange off the block or something like that, not on a bracket like an alternator
If so, standard procedures for getting things loose.
1. tap with a hammer to break the bond with the gasket
and flange. VERY GENTLY so you don't damage the pump.
2. Put a chisel, sharpened screwdriver or similar on the joint between the pump and block IE where the gasket
sits and tap that in. If it breaks the seal and penetrates some then wedge the pump out bit by bit, going around the edges if you can reach them.
3. Spray with PB Blaster to loosen corrosion
. CAUTION. PB Blaster can destroy seals
and rubber parts
so be very careful where you apply it. Might want to spray some into a small cup and apply with a Q-Tip.
4. Heat with a handheld torch. CAUTION. Not too hot or you will melt stuff and careful where you point it so you don't catch the boat on fire. Also oil
on the block can catch fire.