Hi I need help to decode a Vin to know the engine and trans is a 1958 Oldsmobile,

 

You're getting way too complicated. Assuming what's in the car is original, it's a 371 V-8 as that was the only engine offered by Oldsmobile that year.

The only transmission offered was the Hydramatic automatic.

I don't think any of this info was in the VIN back then, anyway, and that's assuming that these cars even had VINs like we think of them today. Others will know better, but I think Oldsmobiles of that vintage had a plate with a chassis number or engine serial number or something like that.