Higher Power Aviation used to add type ratings to commercial certificates. They were bought by ATP Flight School last year so it may have changed. Their web site only says you need the ATP written "if qualified" for the ATP.
In the FAA world a type rating is always done to ATP standards so if you get a type rating on a private or commercial certificate and later get an ATP, the type rating jumps up to the ATP level without another checkride.
I've done training of <1000 hour pilots in a 727, a transport jet is a big jump at 250 hours. There's twice the stuff happening 4 times as fast. Good luck to you.