I just acquired a No.4 Mk1 enfield and it is missing both front and rear sling swivels. I can find the front swivel at various sights but not the rear. My question is , are the front and rear swivel the same. I have the rear swivel base in place. Also I have seen pictures with some No4's with stacking swivels and most without. Were they originally issued with a stacking swivel. Thanking you guys in advance.