is this a standard or automatic transmission?could be an out of balance clutch or driveshaft,wheel bearings?
anyway the tried and true way of adjusting lifter preload on a chevy v8 here in the usa is to warm the engine to running temprature,remove a valve cover and,one at a time back the adjustingnut out until you hear the rocker arm clatter then turn it back in until the clatter just stops,then slowly add 1/4 to 1/2 turn more(make sure they are all the same)to preload the lifter.repeat for the other 15 and you're done!
a few tips if you do it this way...try to find some oil deflectors that clip on the rockers to keep oil from shooting all over your engine bay,keep idle as low as possible,have an extra quart of oil on hand.also clean the rocker cover rails and gasket surfaces of the valve covers thoroughly and apply a thin film of silicone sealer to the valve cover and cover side of the gasket only.on the head side use a thin layer of heavy(clean)grease like wheel bearing grease. this will allow you to remove the valve cover and gasket(carefully)as a unit next time and save you $ on gaskets.also the "spreaders"that fit between the valve cover hold down bolts and the covers are a good idea to help prevent leaks.
they help to evenly distribute the bolt's load.
86 camaro,383,topline vortecs,scat crank,wiseco forged 9.5:1,6"scat rods,comp xs282s,performer rpm,750 proform vac sec,msd in cap, hooker coated 1 5/8"headers,3"flowmaster,700r4,2800 stall,3.42 10 bolt posi,hotchkiss lca's,aje tube k member & a-arms