I own a Mossberg 590.  I am contemplating buying a short barrel kit and filing an ATF Form 1 and complete the
firearm with the host and the short barrel kit once the Form 1 is okayed and returned.

Does anyone know if I am running up against the ATF by having the host shotgun in unmodified condition (e.g. stock 18" barrel)
and the short barrel kit in my possession in the form of constructive intent?  The short barreled kit will NOT be installed on the
host shotgun until it is properly documented via the Form 1.

Any help would be greatly appreciated.  Thanks.

There is no such beast as "constructive intent". The term is constructive possession.
What you describe above is what ATF considers as constructive possession.........when you have no legal configuration for the short barrel.
Get the approved Form1 first, then buy the short barrel
or
buy the short barrel and store it at a friends.

OK; thanks for the help DogtownTom.  I sure appreciate it.