The w/TH does indicate an automatic transmission.
Dwight Southerland has kindly put together a website that is more user friendly than the NHRA classification guide and has all of the critical data.
Please register with Dwight on this website:
http://www.classracerinfo.com/Default.aspx
For your car (1970 Camaro 350 cid / 360 factory HP)
Shipping weight w/ MT = 3341lbs. NHRA P/W factor = 10.44 NHRA HP rating 320
Shipping weight w/ TH = 3397lbs. NHRA P/W factor = 10.45 NHRA HP rating 325
Min. Wt. w/ driver:
D/SA = 3258 lbs. (NHRA rounds down to 3255 lbs.)
E/SA = 3420 lbs.
F/SA = 3583 lbs. (NHRA 3580 lbs)