6M would be right for that model. You can use a D9 as a modern substitute. 6M’s can still be found at club meets or on Feebay. If the old plugs are not broken, re-use them. Cleaned properly and gapped at the spec’d size, they are as good as anything else, and the stock plug from the factory to boot.
Hope this helps.
Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...