One view of "archival" is that it should be reversible.
Using that definition, neither the spray adhesive nor dry
mount tissue are archival. Either way, the print can only
last as long as the mount does, and if the mount is
damaged, it cannot be replaced without severe
risk to the print.
How about 3M Spray Mount Artist's Adhesive? Mounted
works can be peeled off. Must be some using it. May be
as good as wheat or rice starch. Dan