I've got anold Seiwa 12 string acoustic in my shop and it's a very well made guitar (but your guitar is the only other Seiwa guitar that I've heard of)
combination of no "MADE IN USA" (as I understand, MIUSA began in '70 and was used afterwards), relative small size of volute, Les Paul placement on headstock are typical characteristics for that year...could be VERY late '69 but most likely '70
This one is a great player but would make a great candidate for restoration to it's former golden glory
no breaks
get details and pics here
https://reverb.com/item/2128426-gibson-les-paul-deluxe-1970-natural
2700 shipped