With the truck at 160K miles, a $500 budget and no mention of the engine being rebuilt I'd probably fix the exhaust and drive it. As you do, start planning what you'd like to do to the truck, make a plan on parts you'll need, and save money for a staged upgrade. Like Tech says, the first step is to know what you've got, so get the block numbers and suffix like he suggested, and come back with that.

Given that you've said you're not a mechanic, the 160K miles, and your need for a reliable daily driver you might consider that the biggest value might be to save for a would be to shop for an engine, tranny and harness takeout package from a later model truck or car. You can find low mileage packages from salvage yards and end up with a sweet package, parts available at any Chevy dealer, on-board diagnostics, etc, etc.

Another option is to save for a crate engine from Chevrolet Performance - https://chevroletperformanceparts.co...75-base-engine Just be sure to check the specs and select a hydraulic roller cam for long term reliability with today's oils.

While you can get some quick additional power with NOX or a blower, I would not think that either would be a good value for you considering the high miles and need for the truck as reliable daily transportation. Pushing a 150 shot into your old engine might just be the last hurrah - an exciting last ride before a forced rebuild. Just my $0.02, and good luck with the old truck.