1968 hydor-trac operation questions

Hello all, I just picked up my first hydro. Can any one please tell me if the foot brake should work when the engine is not running? The hydro foot brake set up is way different than the shift tractors. Also does the rear end unlock button need to be in the locked position before the drive control lever will move? I have no clue at this point. This unit sat outside for many years. I ran out of pb blaster, so I had to make a trip to tractor supply, got two large cans. The good part was the engine is not locked up, and the rear lock was in the out position, so I could roll the unit for loading and unloading. Just about everything else is locked up, even the key switch. I did not spare the pb blaster. Also came with a 48" deck that seems to be int fair shape to look at, of course it is locked up for now too. Thank you.