Transmission whine, Help please

[Chard10]

I have a 1968 c10 long bed. It has a 350 that was swapped into it sometime since then and possibly the original Saginaw 3 on the tree transmission. Lately the transmission has been making a high pitch whine that can be heard clearely in the cab and seems to come from the dash or underneath. It is not easily heard from the engine bay or underneath the truck but I assume it is coming from the transmission. It starts to make the sound around 2k RPM and up in all gears and it increases and decreases in pitch with RPM. It makes the same sound in neutral and in gear with the clutch disengaged (petal to the floor). Aside from the sound the transmission and clutch work great. No grinding noises, not harsh shifts, no slipping, strong clutch petal feel and engagement. If it were not for the noise there would be no issue. The transmission fluid was a little low, I put about half a quart in it to top it off and the sound remains the same. I have not noticed any burning smells or otherwise. I'm thinking it could be a bearing going bad (pilot bearing was my guess since it makes the noise with the clutch disengaged) and I would like to replace it before it damages the transmission if that is the case. Does anyone have any ideas? I will link a video below.

Thanks