I have a customer desiring to re-line a Winchester. Any recommendations?

TIA,

Bob

who even makes a .45 caliber barrel liner, long enough and with the proper twist rate, for a .45/90?

Try Lee Shaver

https://stores.leeshavergunsmithing.com/

TJ's makes the liner, 18 and 20 twist available. As far as who to do the work, John Taylor in Lewiston, IDaho does a great job on liners. johntaylormachine.com is his website, seems to be down at the moment, just call him at (253) 777-7793

Does he have a hot water heater?

Bobby Hoyt is a legend for his barrel work. But I have used John Taylor several times, with excellent result.
Artisan Name robert hoyt
Artisan Category Longrifles, pistols and fowlers
Company freischutz shop
Address 2379 mt hope rd
fairfield, pa 17320
Map It
Phone (717) 642-8527
Email: freischutz55@gmail.com