Bart, you're makin it sound like anything will work just fine.
But it just isn't so easy..
(343-308)/2 = 17.5thou thickness
I highly doubt 308 brass is even running that thick, so turning here would be only to eliminate variance
(not for clearance).
Also, you do not want to over-size necks. Anything from .0005(fitted) to .003"(total) is plenty of clearance, and keeps sizing requirements rational.
Crank, go Sinclair for turning equipment. It's the best 'system' IMO, including cutters, sizing mandrels, and neck mic, -from one very good source.
This is what you need:
Micrometers - Sinclair Digital Case Neck Micrometer
Neck Turning Tools - Sinclair Premium Neck Turning Kit
Case Prep Units - Sinclair Power Center
Case Prep Units - Sinclair Case Drive and Holder Combo
And go ahead & throw this in the order:
Concentricity Gauges - Sinclair Concentricity Gage with dial indicator
Bullet Comparators - Sinclair Bullet Comparator #1
Calipers - Large Display Digital Caliper
Well that should get you started. I know of no other source with such a complete system.
As far as all other clearances, the same holds as with necks. You don't want to be oversizing ANYHING. In contrast, there is nothing wrong with tight clearances.
To throw in an extreme example, my 6.5wssm has -no more than- .0005" clearance anywhere, right from the git go. So my brass with over 20 reloads still measures exactly the same as first fireformed to. I did not even touch the brass with a die until it's 8th reload!
And that doesn't happen by chance
Well, your pickin your reamer. So make it just as you wish it to be.