I'm swapping a 307 to a 455 in my 1983 98 royal. Should I change the trans.?

 

I would, the stock trans will not like the 455 for very long if you beat it like a rented mule.

 

If the trans worked ok with the 307, and you want the overdrive, install a TransGo shift kit, or CK performance offers a shift kit/servo and governor package. Depending on how hard you beat on it, it may last, or may not. The forward clutch housing is a know weak link. Plan on some upgrades if a overhaul is needed