I just bolted my profile rails right to the T-slot when I built an aluminum extrusion machine. My profile rails were 20mm and it worked just fine but 25mm would have worked even better. You could use a piece of steel flat stock, maybe 16ga, with holes that match the pattern of your rails and sandwich that between your rails and your extrusion. With that method you still have the T-slot to help with alignment and even if your rail is on the narrow side the flat steel will bridge the T-slot valley. That is probably better than just bolting your rails directly to the extrusion.