You can take everything off the firewall except for your map sensor, but you could snag an obd1 throttle body and use the map on it to clean up the firewall some more. They do read slightly different though, but not enough to make a difference.

I wouldn't recommend actually capping the evap line though, fuel emits vapors and changes greatly while being sloshed around and changing temperature.. if the line is capped it could actually pressurize or put the tank under a vacuum. I just installed a breather on mine.