Merry Christmas...
It's been awhile since I've even been around an Iron Duke, but they are nice engines that WILL make decent power for it's size. Normal hotrodding methods pay off on this engine. The only weak spot is the lower end, specifically the crankshaft, that gets to be "iffy" with big power. Somewhere around 200-225hp, you will need to step up to an aftermarket HD crankshaft. Head porting is a needed step in building this engine and will allow any bolt-ons to work even better. I'd start with a header, intake, bigger carb, and a much hotter ignition setup. There are plenty of parts out there, lots of people still race those things from what I understand. Do some web searches for "Iron Duke performance racing" or "GM 2.5l performance racing" or something like that. Call Cliffords performance.
Your definitely going to need a decent mid-range camshaft to get it to do anything special, just keep in mind when choosing a camshaft that the factory crankshaft doesn't like to spin past 5,000rpm, so stay somewhat conservative. You don't want a cam that makes top end power when you can't spin the engine up high enough to use it.
