Help me get into the 12's for cheap

One of my goals with my 73 Swinger is to have it run in the 12's. High 12's would suffice.
My best run is 14.8 at 90 mph.
The car is currently a 318 with what I believe is a stock bottom end. 1 5/8 summit headers, Performer intake and Holley 600 carb. 3:55 suregrip 8 1/4 and I believe a stock converter. I run a 26" drag radial.

I want to keep my current gear ratio because I do drive the car a lot around town and on the freeway.
I want to keep my full interior because I make my wife and kids ride in the car with me.
I don't want to run nitrous
I don't want to spend much money. I understand I have to spend some.

These are the ideas I had.

-junkyard 360 magnum swap. Buy the motor from Pick N Pull for around $250. From what I've read it sounds like I would have to spend close to $2,000 with the new heads, re-ground cam, oil pan ect. It's kinda more money than I want to spend but it should create enough power to get me into the 12's.

-junkyard LA roller 360. I can buy one from Pick n Pull for around $250. I would stay with the 308 heads and I could have the cam reground. Would it make enough power to hit my numbers. It might be the cheapest option.

-new heads and cam on my 318. I think Engine Quest heads would be the cheapest but I would still be around $1,500 with heads, cam and intake. Would it make enough power?

With any of the above options I would still need a better converter.

What sounds like the best option?