1977 Chevrolet Classic - Trans question

Hello, I have an old 1977 Chevy pickup with automatic transmission and 305 V8. Was working fine except for usual leaks. We had a bad ice storm and 2 oaks hit the truck, it was in park without brake on. The switch at the transmission seems to operate thru the 5 positions and before I messed with it would start in ‘park’ then immediately back up in reverse, now even with the shifter rod disconnected it won’t go in reverse at all in what should be reverse. Anything I might be able to do after removing bottom pan. Whatever broke loose. I’am working at putting in a windshield but must have reverse. Thanks.