Good advise.
Last one I did was an K341AQS and the machine shop bill was about $240.
I reassembled the engine myself.
PM me aid I will send you a PDF of the Kohler engine service manual.
Step by step walkthrough of dis and re-assembly of all components. A must have in my estimation.
Your rebuild kit, once you determine what size to order, will include all seals, gaskets, rod & piston plus new valves, I would also opt to the new guides for an extra $20.
All your machinist should need is the bare block, crank, piston and rod.
No need to bother him with any more parts than needed, less stuff to misplace and or loose.
You can deal with the head your self, just search this forum for that process, flattening a head with sandpaper and a flat surface.
He should have the capability to tank, bead blast and inspect the block for cracks etc as well as spec's etc. and be able to tell you what size kit to order.
Got my last kits from this seller on e-bay, look for him.
https://www.ebay.com/usr/bakt4kids?_...p2047675.l2559
Be sure to follow his ordering instructions thoroughly.
Good luck!