there is a bit more involed with turboing a L28 but it can be done even on the standed ecu, the problem is that the dissy needs to be locked or the weights in the dissy need to be removed or more weight taken off them as the advancement in the timing with a turbo will cause all sorts of issues. there are 2 solutions to overcome it, 1) there are some HKS diaphram's for the distributor that actuly retards the timeing as the revs increase insted of advanceing, i have yet to track one of these down they where used with the HKS surge tank setup (tripple webber turbo), or 2) get an aftermarket ecu like wolf3d, megasquirt etc and run a dissy free setup, you can acheive this with a opticle sensor and a 36-1 trigger wheel mounted on your harmonic balancer or on your flywheel, there is a bit of stuffing around and what sort of power you want will depend on what setup you should go, if your chasing 300hp or less the L28 can do this with some 280cc injectors (standed L28et) and no intercooler anything after 300hp thats when the $$$$$$ start.
hope this helps
cheers pauly