Try a rebuilt distributor. It will do wonders to improve the power of your 318. That engine can make a lot of power, but it requires some things. Good spark is one key thing.
If you change to premium fuel, you can advance the timing a bit, and this will also make more power, but it will ping on 87 octane fuel, and get worse mileage when running retarded and lower octane fuel. Higher octane allows more advanced timing, and more power, thus slightly better MPG.
Check with a place like 'Clutches Unlimited' in Midway City, California, and see if they can rebuild your distributor. When you take it out, mark it's location, and point it the same position when you put it back. You would need a timing light to do this job correctly, or take it to a place that can rebuild it, and set the dwell and timing correctly. . .
The 318 can make lots of power. The 360" is only about 15% larger, but has more rotating mass, so really not a lot more power. The newer 5.9L can make over 300 HP, while a older 440 can not.
The 727 transmission can bolt up to the 318 or 360. But if you are looking at donor 440" engine from another motorhome (pre- 1979) you should also get the matching transmission, as the bell housing is probably a different bolt pattern. However the 727 is only a 3 speed, and not known for it's great gas mileage. If you have overdrive, it is not the 1970's version of the 727.
Yes a "RV Cam" will also produce more power, but it takes a lot to change it out, like removing the radiator, so you can remove the water pump, cam chain, and then slide the cam out of the engine, it is about 3' long, and must slide out forwards, through the space that your radiator occupies. .
You might find that rebuilding the distributor, and replacing worn or broken springs is all that you need.
Good luck,
Fred.
