@DTTOLATE
You’ll need a very accurate measurement of the bore top middle and bottom, you’ll need for this is a dial bore gauge, it’ll tell you the OD of the bore and tell you how round it is etc etc,
I send all my barrels and crank to Jim bailey (roadrunners) and he does it for me, I’ve been using him since 2017 for all my dts and mx bikes rm yz etc anything that has a steel liner which all mine was as they was sleeved, he’s very good and last time he did my dtr barrel I did 11k miles before stripping the bike for a restoration it still ran lovely.