Good stuff 44. I never had a T-38 6.5 with an oversize bore that I know of. The early 6.5's had a different twist rate and would usually shoot wild with standard(Norma) ammo. Loading up to a heavier bullet which it was originally designed for usually helps that. I think they were using 190 grain bullets in the beginning.
There are hundreds of thousands of T-99's with no model markings. These are commonly known as "Last Ditch" rifles and if you want a shooter, I would avoid them. The barrel steel was down graded, the stocks were downgraded and had less wood. The buttplates were wood. In general, everything was cheapened. I would consider them safe to shoot, but would check it out good. I had Korean made T-99's that were pretty scarey looking.They are not true "Last ditch" rifles. I only ever saw one and it had an oversize cast iron receiver with navel markings.
Markings: used last three numbers from serial #. The T-38 could have double markings-many were factory rebuilt.
T-38 parts marked: bayonet lug, receiver, bolt, F/pin, safety, dust cover
*more parts could be marked if it was rebuilt
T-99 Parts marked: Bayonet stud, receiver, bolt, F/pin, safety, dust cover
*Late war guns could be missing a lot of markings
It is too hard to just give a solid answer. As you get more familiar with them, you will start to see some weird stuff.