A 305 engine spark plug gap is set at .035 what will happen if the gap is set .050?

The ignition system may or may not have enough energy to jump the larger gap reliably. Also, the spark created may not be hot enough to ignite the air-fuel mix. There are many variables that can affect this energy, mostly contained within the solid-state amplifiers of modern electronic spark control systems. If by "305" you mean the GM corporatized version of the Chevy small block, then it probably has an HEI distributor. The amplifier in the HEI is a little black rectangle about the size of your thumb. It is mounted under the distributor cap. It is also notorious for losing output energy above 3000 RPMs. Newer distributorless systems are less prone to this problem. But most ignition systems lose some energy as RPMs increase.