Spark plugs should be the size of an NGK (brand) BP6HS or bosch W7BP or Champ RL95YC.

Spark plug wire length should not matter, but be careful the extra length doesn't get caught in the steering column coupler.

"Hotter" plugs are designed for easier load operation, to , as you said, avoid carbon buildup. That difference alone should not affect engine temperature.

Ignition timing and valve clearances can drastically affect temperature.

Adjusting valves requires only .016 feeler gauge (the tip soulf be less than 1/3" wide), a 1/2" box end wrench and a flatblade screwdriver. As you slowly rotate the engine (I use a large pipe wrench on the waterpump pulley. Large channel locks work also) you can see the rockers depress the valves, and adjust the ones that are fully released. If you remove the #1 sparkplug, you can stick a screwdriver in there as you MANUALLY turn the motor BY HAND while WATCHING the screwdriver and keeping it from jamming, until the cylinder is at top dead center. If both valves are closed (loose) that is the top of the compression stroke.

But first of all, make sure those plugs are the right size.

Setting ignition timing properly requires a stroboscopic timing light. If you get that, it's pretty simple. Find the 10 advance mark on the lower crankshaft pulley. It's between the 0 and the 20. The other 10 is retarded timing. Mark tht 10+ with a dab of white paint. Loosen the 7/16 bolt on the distributor clamp a little until you can rotate the distributor stiffly. Start and run the engine. ROtate the distrubutor unitl the white dab lines up with the pointer on the cover. Tighten the distributor. 10 to 15 degrees advance is withint the acceptable range, although many people run much more. Depends on the engine, driver, and operating conditions.