Very hard to start

This could be a couple things but we need to start with what it does when it does not start.

I assume it just cranks but what happens if you hold your foot to the floor and then crank the engine? This is called a clear flood start so it will cut the fuel and if the engine starts then we do have an over fueling issue.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/engine-cranks-excessively-before-starting

Below is a diagram of the central multiport fuel injector (CMFI) which is what I assume you replaced? Then when you say it has a mod on the distributor, what exactly would that be?

Have you removed the spark plugs and look to see what they look like?

Below is a also, a chart that will help with this. Let us know what questions you have and what you find. Thanks