Transmission problems shifting

[Dutch4]

Hi all, I have a 71 4x4 burb with the th400. It leaked badly from the shift selector shaft and had a none drain bolt pan. I emptied it and replaced the pan. I removed the selector shaft and replaced the seal and reinstalled the shaft. Put the internal linkage back together and put fluid back. I ran it after I put 3 quarts in thinking it still had a bit in it since I didn’t drain the converter but it took about another gallon. I am sure I put the external linkage together correctly too. Now when I start it. It goes forward where reverse is supposed to be. Any ideas? Did I blow reverse by letting it idle while so low on fluids? I shifted it through the gears while the pan was off and all seemed normal. Thank you for your help. Oh and by the way, the owner said he had the trans rebuilt