Thanks severusx, Split4G didn't seem to have the option to join the files. I did however come across OpenSplit v1.2 http://www.ps4news.com/PS3-Hacks/ope...r-ps3-arrives/.
Here's what I've done...
1.) I transferred the whole game from the ps3 to my external hd using multiman.
2.) I then transferred the split psarc files to my laptop before joining them back together using OpenSplit.
3.) I'm just in the process of using psarc.exe to extract the pak22.psarc ready to go back on the external hd.
All is looking well, think I have it sussed but will report back if I come across any problems.