Hi,
Like to have a Tribologist's opinion, before giving or talking too much advice; there are some good information sites around if you do a web search on the topic, however, various added metals and other additives do various things, if they are not in a cheap oil in enough quantities then those functions are impaired.
The only criticism of new oils, I have found is that apparently they are supposedly more focussed on overall running economy and cleanliness of engine operation, rather than engine wear, which is the thing we are all trying to delay. Also it depends on the type of activity you have in mind a plod or a blast, presumably you want a blast!
Manufacturing tolerances are now so close that some modern engines are supposedly have no need for piston rings! In reality, it has been said that they only put them in because of customer reaction to a new engineering practice. Hence your 0-30w viscosity oils, apparently an oil film, only one or a few molecules thick can pass through the tolerances on ultra modern engines, cheaper thicker viscosities with longer- carbon- hydrogen chains fail to lubricate because of the larger molecular structure and the engine therefore fails through lack of lubrication. However on a 60/70 plus year old machines tolerances are nowhere near as tight, so oil suitability & choice of type and brand is not as limited.
Engine parts and time spent rebuilding are more detrimental to the wallet and soul, than a few more quid on a suitable oil, an oil-cooler and a proper paper- element filtration system modification, would be a good idea if it can be plumbed in sympathetically to the original plot.
Not too cheap and not rip-off expensive, is probably the best advice I have to give, but again it is now possible to buy drums of oil in 120 litre containers, just over 26 gallons for the garage workshop, better oil at discount prices and if you look @ how oil is increasing in price this may be the best idea, I saw some on offer @ £95 last year from £135-£140!
Cheers
JBW
