draining L+R

Hello I have a question about draining water for the winter. i have 2 boats.
Have a 351W-L 1991 and have a 351W-R 1974. Engine on the leftside has a small rear-lower plug to drain the left cilinderbank.
Engin on the right has a front-upper plug, so what about the lower side of the left bank.
I tapped the 1991 plug came out easy.
The 1974 has toast plugs, so i removed the left freezecap first and drained the block, so the block should be empty. Decided also to take out the right lower freezecap, to my suprise i think a full gallon came out.
So wenn you pull a normal drain procedure only the hex plugs a gallon stays in the block.

Is my a$$ume right or am i missing some steps?

Missing the second plug.
On the lower block the leftside is clear, its a hex plug about 1/4".
On the right side behind the starter, there is a similar thread hole, can look in to it about 1" deep, but dont see the hex to turn it out.
Its the same on both engines.
Am i missing somthing there?

the drain on the block for the left side/pa$$enger side is towards the rear of the block. On the otherside/drivers it is towards the front of the block, they are not located in the same postions on each side of the block.

to help drain the drivers side just drop the tongue of the trailer as low as possible so that it makes contact with the ground flip up the wheel/jack if needed. You can also get a bra$$ fitting and a piece of hose and suck it on that side. If you going back with car anti-freeze it's realy not an issue.