263W Lionel Prewar Tender Whistle Availability?

A newer style air whistle will fit, but it has to be elevated on a special bracket so the bottom of the tender shell can slide on top of the frame. You could probably fabricate one; they are not common.  If I recall, they are about 1/4"-3/8" tall.

I've worked with many Lionel whistles both prewar and postwar.  I can find no differences, before they went to plastic cases in the 50's, except for the position of the mounting holes.  I recently repaired a 390 tender that originally had a banana whistle using a postwar whistle.  All I had to do to mount it was drill one hole in the tender frame.  Electrically they are identical.

A word of warning.  Don't get the later WS-175 that was found in a few 50's tenders and was mounted horizontally.

From the screw hole pattern, it originally had a banana whistle. You can use a common postwar whistle unit from a old coal tender the mounts vertically. But you will need to fabricate a bracket to raise the whistle to clear the round sides of the tender. Like Jon said.

Here is an old thread but it applies to a current project for me.
I’m trying to put a w-125 into a prewar 265w tender that had a banana whistle.
I understand the suggestions above but in doing that the air holes in the frame and shell do not line up with the newer postwar whistle.
Does it matter? Do I need to cut new holes?

OK, here's a follow up.

I mounted the W-125 by drilling 2 new holes in the tender base and in a position that didn't restrict the inlet/outlet of the whistle as best I could.  No mounting adapter was necessary.  I cut no new air holes for the the whistle.  Put it on the track and listened.  Each postwar whistle is always different due to condition.  But overall, it seems the whistle is a little muted.  However it is a distinct postwar whistle that I can hear from 15 feet easily.

So I see no need to cut any new holes.