Whether you download the GCD file from the Garmin link i gave earlier or from the Perry site you will get the exact same file, only difference being the name [from Garmin it's 'B2077000M.CGD' and from Perry it's 'nuvi2xx7and2xx8C4_830.gcd']. Both have MD5 hash of A17FC82419D30B49BC9920DD3C04119A.

If you wish to be absolutely sure that your 240 uses 2xx7/8 C4 firmware then do this:

(i) See if you have a file named 'GUPDATE.GCD' or 'gupdate.gcd' in your 240's .System folder. Check here how to find it if a folder named .System isn't visible: [Only registered and activated users can see links. ].
OR
(ii) If there isn't a GCD file in there, look in it's Garmin folder for GarminDevice.xml. Open it in a text editor [NotePad is fine for this], search for '<SoftwareVersion>' near the start of the file and change the 3 numerals following it to from '830' to '820' [no quotes], save that and without disconnecting from PC open [Only registered and activated users can see links. ] and let it check for a software update for the unit. It will offer you V8.30, accept that and let it download GUPDATE.GCD to your device.

Move the gcd file to somewhere on your PC to work with, make a backup copy too, and then you can patch the gcd file to make 207701000830.rgn to flash in preboot [your unit's HWID has a GSV check in fw so initial patch cannot be done with a gcd file]. Carefully follow the instructions in initial post here: [Only registered and activated users can see links. ].