'68 Dart with a 318 LA - Build Options

If you're not trying to give it a major boost in horsepower, I'd keep it simple. Keep what you have, a few minor add-ons, and freshen it up. You mentioned keeping it reliable and inexpensive. In that respect, I would want to keep it fairly stock and easy to remember which parts to buy in the future. Having parts from all sorts of year and model sources leads to confusion, wrong parts ordering, and having to modify things to fit. On a mild engine, forget the headers. All the Hedman headers I've seen fit poorly and hung down too low, to where they always had smashed pipes from bottoming out in dips. To me, the slight improvement in performance wasn't worth the hassle in installation, interference in working in the engine compartment, and cooked plug wires. Keep the compression ratio low enough to run pump fuel, 340 purple shaft cam would be fine, double roller timing set, high volume oil pump, and call it a day. If you're looking for performance, do a 360 swap, and all the conversion stuff required to do it. Shift kit the 904 and a maybe a slight stall increase. Your next concern will the rear end once you get the engine/trans done. A slant 6 will blow up a 7 1/4, so, it's just a grenade waiting to go off with a V8. An easy performance upgrade (and related decrease in fuel economy) would be to go with a stronger rear end, and a lower gear set. You'd be amazed how much extra acceleration power you can get by installing 3.55 or 3.91 gears, even with a stock engine. Your freeway cruising RPM will increase doing that though.