What jig or template can I use to be able to drill in place through horizontal fence boards to be dead on holes in a steel post

drill

Imagine that I need to drill through boards that will be set horizontally and they will need to be attached to a post like below. For simplicity I will say that the boards will sit on top of each other and will be installed from bottom to top. This is a horizontal fence

The steep post has .20" diameter holes spaced 1" from each other
As in the picture on the other side there is a piece of 2×2 that is already screwed to the post. The post will be sandwiched between the boards and the backer 2×2 (see the detailed picture, zoom in at the bottom of this post)

I think I need a jig that will consist of a piece of wood with three short #10 machine screws that will lock the jig into position, vertically and then predrilled holes in the jig, holes that I will use as guide for drilling new ones
Yesterday I tried a similar approach but with screws …their tip is very sharp and the jig (made slightly different) had errors and I ruined a couple of boards

Here are the specs and the instructions for this type of post

Any other I idea ?

Update: here is the fence I am trying to build
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Best Answer

Pegboard comes predrilled in a 1" grid, just like the holes on your posts. Cut a strip out of a sheet, line it up with the holes on the post, and attach a reference block to the top. Et voila, instant story board.