SERIES 3 PERKINS (huge engine)

Hello all.
My nipper has bought himself a series 3 109 safari on a 72 plate for £50, comes complete with a perkins 3.8 (p4.236) mated to a standard s3 box.
Is this a comon conversion for series, and what are the expectations i.e. top speed, fuel consumption, power etc.
i have a 3.3 p4.203 in my series 1 (88") and keep a stock of half shafts for its s2 axles, is there a recommended stock to hold for a series 3 with the 3.8.
Any comments appriciated.
cheers
bodgit0_0