Welcome to Moparts.
You will find, nearly anything you might ever want to do with your car has been covered here before. For all practical purposes, almost all info you find covering any Mopar between 38 or 39 and 54 will be able to be applied to your car. There is a bunch of info on here covering the 46-48 cars, most of that info applies to your car.
The flathead 6 was a good reliable motor. It can be upgraded to increase the power output, as long as its in good shape. Splitting the exhaust manifold and adding a second exhaust exit to make your exhaust into dual exhaust helps a lot. You can also split the intake manifold and add a second carb.
Probably your biggest problem from a performance stand point is the transmission, its killing your performance. Installing a same vintage standard shift 3 speed or a vintage standard shift over drive (if you can find one) would make a huge improvement, and with the correct pieces it should all bolt up. I would presume a modern automatic transmission can be adapted to your motor, but I wouldn't know who or where such adapters can be found. A modern rear axle with more road friendly gears (your car likely has a 3:90 something gear in it) Gearing in the 3:23 range would get you up to highway speeds, but those gears are not available for your rear axle. The rear axle exchange would make working on the brakes a lot easier as well. 66-70 B body rear axles are a very close bolt in fit.
The front suspension on your car is the same basic setup that was used from the late 30 through the mid 50s. Look for information about 46-48 Dodge, Plymouth and Chrysler suspension here on Moparts, there is as ton of info covering these years and that info will apply to your car as well. The single biggest improvement in the handling on your car is to relocating the front upper shock mount. That single thing makes a day and night difference in the ride and handling. There is a "kit" available that needs to be welded onto your frame, but its a pretty simple procedure, and would be worth the investment of paying someone to do it.
You can get a disc brake conversion for your car that really improves the brakes too.
Disc brakes, split intake and split exhaust manifolds at
www.rustyhope.com I think he may have the shock relocation kit as well. I'm sure others will step up with some more web sites. Gene
