Comparing the RPS for the Series 3 FFR (RPS02090) with the Perentie RPS for both the 4x4 FFR and the 6x6, the 28v Generator is the same as the type fitted to both vehicle types (Part No DE290010001, NSN 2920 66-095-0364), although the mountings vary due to different engine fitments.
I have a Perentie 28v Generator for sale if you like, but you will need to find the Series 3 engine bracket.
Where on the Series 3 and Perentie the 28v Generator is an auxilliary unit extra to the 12v Alt, it might interest some to note that the vehicle generator (ie the ONLY Gen/Alt on the vehicle) fitted to the NZ Army's 24v Series 3 Stage 1 V8's is also the exact same Genny as the 28v for the Perenties, indicating it saw much wider application than just the one vehicle. 24V Gennys for the NZ V8's are getting hard to find, but I've sent a few Perentie ones across to fill the need (and the bank acc!).