Engine decoding

[RodnRudy]

I'm sure you guys get asked this question a lot so I'm looking to you for help. I bought a 68 SWB Chevy fleetside that originally had a 6 cyl stick. It was swapped for a V8/350 auto. I've tried to decode the engine through internet sites and here's what I've come up with:
Engine code- T0105CMJ I get, Towanda, Jan, 5th, and here's the hard part
CMJ could be 1974 350 160HP 4bbl T400 Police, or 1975 350 145HP 4bbl THM350/400 Federal. And lastly 1980 305 Auto.
Now I don't think it's the 305 because the other number stamped on the block is: 16J199806. I believe this is the number that was stamped on the engine when it was put in the vehicle and the 1 represents Chevy and the 6 represents 1976 and the J is Janesville plant the other numbers the vehicles serial number.
Is everybody confused now? Oh and it has a two bbl carb on it but that could've been changed. Surely that engine didn't sit on the rack and not get used till 1980?