Suntour Cassette - Shimano Freehub Compatibility?

I have a mid 1980's 105 Freehub (6 speed, originally).

Are the splines compatible with a Suntour 'PowerFlow' cassette? Is the cassette (7 Speed) narrow
enough to fit on the freehub body(6 speed). I recall having munged this in the past with a shimano 7
speed cassette, without entirely satisfactory results. The threads on the last cog barely engaged,
but it was rideable, for a while.......

Thanks, Rob