id say still stick to the 15-30 oil its fine, i run it on my ea which has done 206,000km and i get no lifter tick or nothing, move up higher in weight if you start burning oil or getting ur lifters ticking id say.
check that your control joint arms have the botls still tight on them as overtime they can strip them selves and loosen, may even be safer replacing them, another thing would be replacing your bushes, they wear very easily and all of these things are simple jobs you can do on ur garage floor.
pacey's you would expect to pay $450 supplied and fitted, when they fit them they cut the cats down pipe shorter so the extractors can fit, i wouldnt bother replacing the cat unless your one of those tree huggers no offense.
EA Falcon, 5 Speed Manual.
2.5 Inch Exhaust, lowered 3 Inch's,
17 Inch Wheels, SuperCharged 10Psi.
Ported Polished Head, XR6 Valve Springs,
Bigger Valves, Stage 2 Cam. Water Inj.