So the snail won the drag race...

Tiny exhaust pipes + 10-year-old cat (meow!) moves exhaust restriction higher on the list. If you wish to address this in the best possible way, your headpipe should be 2-1/4" diameter and you should put in a cat (meow!) equal to the task being asked of it. Yes, you can buy a cheap little converter very easily. They are junk, warranted only for 25,000 miles and minimally effective even on clean-burning engines. But for a nonfeedback-carbureted vehicle like yours, you need a heavy-duty, high-load converter -- anything less is a waste of time and money and will quickly need replacement again. The trick here is to get a California converter. These have to be type-approved to much stricter regulations that require much longer durability, so you get your money's worth in the long run. The one to buy is this (that's a very good price on it, too -- might want to pounce on it before the price goes back up, and put it on your shelf for when it's time to install). Another good idea while the converter's being installed is to wrap the headpipe with this, which will do several good things: it will keep the exhaust extra-hot on its way into the converter, which facilitates maximum converter efficiency and reduces the likelihood of converter damage by improper fuel/air ratio. Also it keeps the underhood temperatures cooler, which is beneficial for driveability.

"Really quiet for an engine with mechanical lifters" suggests the tappet clearance may be too tight, which will take a big chunk out of engine performance.

Just dropping in a new timing chain and sprockets, lining up the dots, is a big gamble. The location of the dots isn't anywhere near as exact as we wish it were. You really(!) want to take the time to degree-in the camshaft. Given the car's configuration you'd benefit from advancing the cam from its nominal position, and you'd benefit even more from an RV10-RDP cam swap, (big wakeup for a stock or stock-ish \6).

If you want to keep things as stock-looking as possible, keep your eyes open for a NOS Holley 1945 for a Dodge truck application. Those have bigger venturis and are generally less strangled. Take your time and wait until you find a genuinely new one; "remanufactured" carburetors are junk. And do get with DusterIdiot about a recurved distributor.

But if you're on a super tight budget, you may well just have to stick to the easy low/no-cost stuff like a careful valve adjustment and tip-top careful tune-up and live with the nature of the beast until you can afford to "re-nature" it more comprehensively.