I have an aluminum case overdrive transmission that I would like to convert into a cast standard case.

Can this be done?
Will cluster shaft fit
Can the 308 input bearing be changed to a 307?

Any input would be greatly appreciated

Yes. All gears and mainshaft MUST be swapped together. Use the cluster pin from the cast iron case. Also use the 307 bearing and corresponding front bearing retainer. Some tailhousings used a different bearing. If this is the case, use the bearing from the iron tailhousing.

The only caveat here is that you can't swap a long tail OD mainshaft into a short tailhousing A/F body

od truck is same as a b/e length

The cluster shaft will work but it's a little short and you'll want to seal it somehow or it will leak ... been there got the spot on the floor to show for it .