Yesterday, CelesteBlue released Memecore, a port of h-encore for older firmware 3.60. Support for 3.5x firmwares is scheduled for the days to come.

Memecore is the successor of memekaku, that enabled us to install henkaku on older firmware such as 3.55. This release announces the end of memekaku support and a new way of exploiting your PS Vita (using the h-encore exploit) so it’s more reliable than memekaku. And guess what? You can also use it on 3.60 so now you have both the browser exploit and the h-encore exploit.
If you have problems using the web browser to install henkaku, you can now count on memecore. This release enables us to rediscover old exploits such as rejuvenate, failmail, TN-V while keeping HENkaku, but will also helps developers to reverse engineer old firmwares. This release was possible thanks to the latest release of h-encore 2.0, which has updated the kernel ROP chain to use gadgets that are also available on lower firmware so it is easier to port it to said firmware.
The developer credits TheFloW for h-encore exploit and Princess of Sleeping for cross-FW offsets porting
Download Vita 3.60 Memecore

You can download memecore from the developer’s github here.
From CelesteBlue: You can use the provided system.dat, or build on Linux it by typing ‘bash ‘.