Jamerson with a P bass right ?
No, that was done by Wilton Felder in L.A. All the Jackson 5 hits were done there. Felder played on a number of their early hits, Ron Brown and Don Peake played on some others. After Jamerson moved to L.A., he played on a few of their later album cuts, but no singles.
Somewhere a few years ago I saw an interview with Felder where he mentions what bass he used but I can't remember now what it was. Maybe a Tele Bass.