[dipso]

Does the garage leak? I would be a little concerned with the slope.
Any water that gets inside is designed to follow the grade down and out the door. Since you are putting a wall where the door used to be there is no exit.
That is not good.

How good are you with that quickrete. A really good idea would be to put down a layer of brick or stone wall cap first with the quickrete. Then anchor your 4x4 to that. Then build up as planned.
That would give you 1" to 2" of brick or concrete to have the water settle against.

You could use your 1/2" masonry bit to drill some drain holes in the brick or concrete base. Or even lay them with some spacing every 4 or five bricks.

If you ever noticed, most garages are built on a curb, not on the ground, even though it looks like yours is on the ground. Maybe it is old? Maybe that is how they do it in Denver?
Drainage is good. Especially on the low side.

I know you don't want to buy any tools but do you have a hammer drill?