I'd add the 8 oz, split between compressor and R/D; then turn the compressor like you stated. I'd avoid "seal conditioner"; it sounds like you've "done it right", so skip the Interdynamics Inc. additives.

Pull a deep vacuum; really deep with PAG, to insure the moisture is out.

I prefer POE type oil (the new stuff) on a conversion, but others disagree......

Charge into the vacuum with ~80% of the R12 charge (I'll let you compute); then keep adding an once or two at a time; monitoring vent temp and hi and low pressures with gauges.

At ~85% of R12 weight, you should be really close to done.

The oil is in addition to the weight of refrigerant.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)