Oiled plugs

4.2 litre
No 6 and 8 plugs fouled with oil.
Heavy smoke under accelleration out of LH bank exhaust, split system no crossover
Had time only to do comp test before away to work for a few weeks
Comp all cylinders cold WOT, are 155 to 160 psi.
thinking about what may be causing it so can into the problem when back home