You can make your 305 run 345 with a compleate rebuild, that PI 350 makes right around 300 the way it is, your 305, 145 stock ( if it's an EFI, it's less with a carb ). I'm not saying a 305 isn't a bad motor for a daily driver but, your obviously wanting some go power cause you want a posi diff from a caprice cop car. Add up all the compenents too make the 305 run at least 300HP with no question, then weigh the cost with that and the 350. I'm not saying it's not feasable to get 300 out of a 305 with no question, but it would cost more than your '83 parasienne is worth, the 350 arleady being a high HP model, is a more logical choice. The main diffrence between a 350 and a 305 is the bore, the stroke is the same, which gives you the low end grunt that you are talking about.