Artic-Trans am

so now I did the funny thing.
I blew up my reverse on my 350 trans.
the trans is a built like this
Manual valve body
reverse shift gear.
w/trans brake.

now, I guess it is the trans brake that caused the lack of reverse. I burn the clutch or something.
The trans started to fail when moving the shifter in R. but by using the trans brake I made it out of the situation "there and then". but now after some days even the trans brake can't make me go reverse.
I can also feel a bad shifting in 3'd gear
1 and 2 gear are still ok.

The question is did I brake the "low reverse roller clutch" or just he clutch pack!
is there a way telling this form the fail, or do this need to come apart before I know for sure?
then, where and what part should I by?