L27 performance/modding

Does anyone know of any cost-effective modding for a 91 L27 3800? Yes i know the engine's pretty powerful as it is, but i'd like to squeeze a little more out of it. It seems that everything i find on the web is about the series II and series III, not really much for a series 1. also I wanna keep the car street legal so NOS is kinda outta the question. the only things i've come up with so far is a cold-air K&N intake, and dual flowmasters exhaust. I'm looking to boost it up to around 300 hp, and i'm trying to find the cheapest way to get there without sacrificing too much on the reliability and mileage of the car. thanks.

or does anyone know of any worthwhile performance parts for it?