Old guy, new love

Last fall, I stumbled across a 1958 Plymouth for sale on social media. I honestly thought I’d never be in a position to own one but I took a chance and was able to purchase from a good guy who resided north of the border. I’m no mechanic so I’ll be looking to the folks on this site for some much needed direction (please save the ‘blinker fluid’ comments for the younger crowd). She’s a stripper (the car, that is) as most Plazas were. The body is in reasonably decent shape (I suspect there is filler lurking in spots) and there are only a few small holes in the floor pans. None in the trunk that I’ve seen. Interior was redone years ago and the entire inside was painted dark blue. The car was originally iceberg white with a bluebonnet blue roof and insert. It’s currently white pearl with a dark blue insert. A local mechanic performed a complete tune up a few months ago but she still doesn’t run very well. Rough idle at stoplights but runs out ok up to 50 mph. Above that, it feels like I’m driving into a head wind…not missing, but not running smoothly. She has a 318 two barrel with a power flite tranny. I don’t have unlimited funds so this will be a passion project for the foreseeable future. The first thing I’d like to do is get her running well. Thought about a crate engine as there are so few shops that will do machine work and even fewer that will work on a classic car. Not sure if the power flite (904?) will function properly with a higher HP motor but I’ve read (on this site) that the rear will likely require a change.

image.jpg Thanks in advance, much appreciated.