An idea:

Measure Tool.

Double-click the measure. The dialog box Measure Attributes appears.

Change the Measure Width to something bigger, e. g. the double width.

Click OK.

Now you have more room in the measure, and it should be possible to click the grace notes in via the Simple Entry Tool.

NB: It is probably a good idea to de-select {Automatic Music Spacing} - to avoid that the measure width shrinks again, before you have finished entering the grace notes.

I played with it for a while. The only way I could get it to work, with stems as you show them, was by putting the primary notes in layer 2, and the grace notes in layer 1. Otherwise, things kept going funky with the tremolos and the beaming. And then, a bunch of respacing with the special tools. (Remember, it will all print black!)

I could get it to work.

The order you do things, is important:

1) De-select {Automatic Music Spacing}.

2) Enter the two measures with grace notes, but without running the plug-in Easy tremolos (= enter the tremolo notes as quarters).

3) Apply Music Spacing, and Update Layout.

4) Delete the grace notes. The spacing will not change since {Automatic Music Spacing} is off.

5) Create the tremolos. The spacing will not change since {Automatic Music Spacing} is off.

6) Enter the grace notes again.

You may have to join the tremolo beams again.

By The Way:

You tell that you are “trying to put it in Finale to create a rehearsal track”.

For the rehearsal track you do not need the layout.

You could create a “playback only” version, where everything is written out in regular notes (= no tremolo notes, and no grace notes).

Nice work, Peter!

Thank you very much for the help!

For what it's worth, I enter grace notes from right to left (ending note to starting note).

I just clicked in four grace notes, at a random pich. Then I want back and arrowed them to pich. At the time, it just seemed to be the easy way.