The one other scenario which i can visualize is usually that it could be a regular Model 70 barrel and motion using a substitution XTR stock. That is unlikely although...I suspect that it's as you describe, an unmarked XTR. The heart with the rifle will be the classic Model 70 https://winchesterfeatherweight86431.pointblog.net/the-single-best-strategy-to-use-for-winchester-model-70-classic-featherweight-67782800