This stamp came from a collection that has yielded several incorrectly IDed stamps. The sides look like them may be trimmed and in a few spots show what may have been perfs but not sure. Watermark was not easily seen. Perfs seem to measure OK but again not totally sure I cut and pasted top to bottom for comparison. If not 351 - it could be 347 with added top/bottom perfs or 335 with trimmed perfs left/right. Would like your input on which base stamp it might be.
Thanks in advance for your time.