Prop and strut

40” shaft would be original. There is no min... the smaller the gap between strut and prop, the better. Figure 3/8” to get a puller on.

I wouldn’t use that to determine proper engine placement though... there are better ways to do it- though you’ll need to mock it up in the boat.

3/8” or 3-3/8”?

Duane in Indy wrote: Oops Sounds like a lathe job in future to me

I'd say it's more like a engine adjustment. Per the list, a Mustang should have the 40" shaft so, the engine needs to be moved forward.

That measurement doesn't surprise me too much. Having owned and torn apart several mustangs, I've noticed that they tend to have a long tail aft of the strut.
If the engine is back in its original position after the stringer replacement, I think your best bet would be to shorten the shaft on the coupling end. A maximum of of 1" between the strut and the prop would be best. My old '70 mustang will be retuning to me in the week or so if you still need measurements. However I know it has a long tail as well..

I would like to tell everyone that is trying to help that I went from the old style mounts to a set of commander mounts I bought from someone on this site

You need the measurement from the log to the trans flange from a similar boat and that is where the engine should be located regardless of what mounts you have.