Son, yer askin' the question the wrong way 'round!
The question is whether a puny 300T has the ..... to drive them righteous 140's!
Trust yer ears, but do remember that them JBL's is probably older than you are.
...and ifin' ya don't believe what a great cab ya got - just put it up for sale!
Seriously, unless something is blown, you should have a really great, great set up.