Easiest/Cheapest way to a 4bbl 318?

Id go with the Edelbrock Performer, LD4b (discontinued- look on Ebay etc), Weiand Stealth or Action Plus. Whatever you can find that's cheap.

With the super low compression stock 318, you need torque/power right off idle.

I ran a 670 street avenger on my 71 318 with an LD4B. Its what I had laying around and it worked fine, and it'll be a better carb for if/when you get a bigger motor or a hotter 318. Its a vacuum secondary, so it'll sort of size itself to the car. I didn't have any problems with mine, and it felt like a whole different motor with the 4 bbl carb. A different slow motor, but much improved.

Exhaust and cam will help, but you *really* need to resist the temptation to get a big cam. Your motor has very low compression and won't work well with something that needs to get wound up to make power. Hughes sells a cam for these engines that is supposed to work well (I haven't tried it). The smallest Lunati might be ok.

Biggest bang for the buck at the track will be gears, converter and tires.

Good luck

Steve