How to tell is my motor/tranny will support reverse

I just bought my kfx450r today. 2008 model. The rev lever is still on the right handle bar. How can I tell if the person I bought it from put in a race motor setup? Looks like it has been modified from stock. What can I look for before I blow the case if I get my hands on a reverse cable and hook it back up?

Also the rear brakes have been removed. I have the disk on the axel and the rear brake lever and the caliper bracket.

It also seems to have a weak battery. I'm gonna replace this for sure soon.

I'm a noob, sorry

Thanks