Lseries is old school diesel and although a bit noisy, pretty bullet proof.
Decat, better breathing, s/s exhaust from cat back, boost up a bit, plus SDi injectors, and a remap from Reidys in Yeovil will see 158 bhp and 232 ft lbs torque.
Dont know about Streetwise.
Dont think they are the same as a 25, though. but might be wrong.
you looked at the buying guide for derv.
http://www.themgzs.co.uk/vb/showthread.php?t=11326