PCB Builder Gerber 274X file extension types

I’m using Mentor Graphics Xpedition to generate output artwork in Gerber 274X format. The only file extension produced is .gbr.
But .gbr is not listed as an acceptable extension (incorrectly referred to as a format) on the PCB Builder page.
Is .gbr an acceptable file extension for my 274X Gerber format?

I suspect you just need to rename your files so that the extensions match the layers shown in the file formats list.

Silk Bot.gbr → MyPCB.gbo
Silk Top.gbr → MyPCB.gto
SM Bot.gbr → MyPCB.gbs
SM Top.gbr → MyPCB.gts

Usually when the g(b/t)? file extension pattern is used for designating Gerber layers, the signal layers are gto & gbo but I don’t see them listed.