Not a gunwriter, but:

If you have a .308 WCF or .300 Savage die you might use it as an intermediate step to make things easier.

Turn the outside of the necks after necking down, you will likely have the dreaded donut since the shoulder is becoming neck.

To determine how much to remove, be guided by the OD of the neck with a seated bullet compared to a factory round.

Annealing and Imperial Sizing Wax are your friends.

'Four legs good, two legs baaaad."
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"Jimmy, some of it's magic,
Some of it's tragic,
But I had a good life all the way."
(Jimmy Buffett)

SotG