I'd try to find a B230ET (ie: non-catylitic convertor), as its gives you more BHP :)
Take a look at
www.turbobricks.com as there is a guide to the various versions of this engine somewhere there. A B23ET (from a 240 / early 740) has a stronger bottom end (forged on the 240?) and thicker con-rods, as well as a garett T3 on the early 740 at least. An early B230ET has weedy (9mm?) con-rods and is not much good for big-bhp, but later ones (88-on?) are much tougher (13mm?)...the trick is to find one of the last B230ET's....just before they became the FT.
Sadly my project is off on insurance cost grounds...for now...(although I might save up!)
cheers
James