First, this should be in the SMB and SMP.
Second, can you explain why your customer requires R77.20.60 versus the latest version?
If it's due to a technical issue, then you should contact the TAC (especially if it's urgent as your message tag suggests).
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As far as I know, the backup can only be installed on the same version it was taken from (or possibly a later release, but definitely not earlier).
The backup contains a copy of the configuration as a sqlite database, among other things.
It does appear the version the backup was taken with is coded into the database.
Using sqlite .dump, I can see the following:
CREATE TABLE system
name text NOT NULL,
vendor text NOT NULL,
PRIMARY KEY (name)
INSERT INTO "system" VALUES('Security Gateway 80','0.0.1-b0','R77_990172392_20_80',NULL,'Tue Jul 3 14:28:30 2018','Check Point',NULL,NULL);
I also see the image used in: addtional_settings_tmp/pfrm2.0/etc/prev_image_info
Presumably, you could modify the above to the appropriate value, recompress the directory, and attempt to restore against R77.20.60.
However, if there are differences in the database schema between R77.20.60 and R77.20.80, or there are other places where the version is specified that I didn't find, this won't be enough.