Anyone know the history of my Ocean & Earth 80's gun board by R. Sharp

Bought a board from Coffs Harbour last week dimensions 8'4  21 1/2 and 2 2/5 older style gun with a single fin that slides up and down with allen key. I've only been surfing for abit over a month and it seemed to nose dive easilly as there isn't allot of a concave shape. Did i buy a dud? or is it i'm too heavy at 99kg for it.....any info on these types of boards would be appreciated..

A bit over a month and you bought an 8'4 gun? That's the problem right there. You definately won't look cool, but a minimal will work a lot better, for a 99kg bloke, 7'6-8' would work well. Sell that gun.

some photos