There's a good reason for remaking the seat tube to accept a standard seatpost. Few 26.8 and 27.0 seatposts are of good quality and easily adjustable. The milling needs to be done only one and its
forever.

Peter White of Peter White Cycles has a few observations about the issue:

You can buy 26.8mm and 27.0mm seatposts. But they are all low quality with only a few fixed tilt angle positions for your saddle. You very often can't get exactly the right tilt for your saddle and your rear end. For that you need a true micro-adjust seatpost, with no click-stops limiting the angle of your saddle. There are plenty of seatposts with a true micro-adjusting clamp, but they aren't being sold in 26.8 and 27.0 sizes, except by Nitto. But Nitto will only make these posts if a customer orders a minimum of fifty posts, in each size. You can't order 25 in one size and 25 in another to make a fifty post minimum order, you must order fifty of any given size. For this reason, not a single distributor in the United States has been willing to order these sizes from Nitto, even though there are plenty of good quality frames out there that require these sizes.

So a little work on the seat tube will allow a high quality seatpost to be installed.