Agreed on all the above, except use a gearbox oil (EP 90 or 80W90) that has no higher a rating than GL4, as the EP additive in GL5 grades can cause corrosion to the gearbox bearing surfaces - SRM advised me on this years ago and I've read it elsewhere several times since.
Opie Oils website has plenty to choose from. I use Castrol Classic EP90 myself but there are plenty of others available.
If you're looking to fit an oil filter on an A65, Paul Goff offers a kit which mounts a Norton Commando
filter from one of the rear engine mountings. Not too difficult to do and well worthwhile. It's quite inconspicuous and offers easy filter changes too.