Modification of K-member idler arm mount advice

I'm fixing a 69 Dart that was in an accident and needs a new K-member. I sourced the red one a while ago and welded all the seams but when I went to install it the idler arm mount of more different than I thought.

After some reading I think that the new one is a 67 and therefore has another idler arm, everything else seems the same (apart from passenger engine mount).

I need to move the idler arm mount from the old member to the new one.
Does anybody have any advice on how to make a jig for this? Should I use the lower control arm pivot and the steering box bolts as jig mount points? It obviously needs to be close but how precise are we talking about?

I have considered making a jig that uses the centerline of the hole in the "old" mount to line up the hole in the "new" mount and then measure for height but maybe the centerlines are different.

Any advice is appreciated :)

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