Engine swap 318 to 360

If you use the van 727, the governor will be wrong.
If you change the rear gear ratio, and the governor is currently correct, then it will be wrong.
The TV pressure can be adjusted to compensate for just one ratio either way, but the result is not always acceptable.
This is a great swap; I've done it several times.
If nothing else, it allows an easy 10 to 20% less gear for similar take-off performance, and about one-half the percentage difference in fuel economy....... before the gear-change.
The 360 2bbl/Holley, if you reuse it, is a lil bigger than a Carter, but is usually calibrated very lean, and the transfer slot to mixture screw setting synchronization will be almost critical. This carb can be made to work, I mean it's just a carb, but it will take a lot of work for very little gain.
I have installed the factory 318 small-port intake and Carter carb with good success.
You will love the off-idle torque increase.
For low-rpm torque/ fuel economy, with a modest loss of top-end power,.... you can even use the 318 heads, and even the 318cam.
That factory cams are, IIRC;
240/248/112, compared to the 360 at
252/256/112
At split-overlap the Ica's are 50 for the 318, and 58 for the 360 2bbl cam.
That difference, at 8/1 true Scr is worth about 10 psi CCP(Cranking Cylinder Pressure), But a bigger gain is the Low rpm performance increase of 13.5%, from stall to about 3500 rpm, due just to the greater pressure.
Furthermore , the Power-stroke goes from 118 on the 360 to 122 on the 318. While just 4* difference, the 318 cam is calculated at split overlap=2* advanced whereas, the 360 cam at split-overlap is 112/straight-up, so there is room there for even greater results, by retiming the cam.
While just 4* different, it will still show up as better fuel-economy in steady state....... and with the higher cylinder pressure, lean-calibrated carb, and with proper cruise-timing, may/probably will get better fuel-economy everywhere, except possibly in town, which has lots of stop/starts, depending on your driving-style.
Like I said; I've had good success with the 318 top-end installed on the 360 short.
Either of these cams hardly care about headers, if the dual exhaust is free-flowing, with say 340, or Magnum log manifolds; but; Headers will NOT hurt it.