You must not compare modern engines with your 'B' series. When the engine was first designed, it did just 6,000 miles per GALLON of oil at 40mph; and only 500 miles per GALLON of oil at 80mph. If you could get up to 80mph, your Austin A40/A50 would do just 62 miles per pint. Normal running with a NEW A50 engine gave 750 miles per pint.
The high speed oil consumption was improved to over 2,000 miles per gallon by better piston rings in mid 1955, but the normal consumption has never really got any better. So a half worn 'B' series is doing very well if it uses one pint of oil to every 350-400 miles.
A worn out 'B' series will blow most of its oil out of the breather, and via the rear crankshaft seal, due to piston blow-by. I have had friends who put a hose on the breather pipe from the tappet chest, the other end into a can. After long runs, they would empty the oil back into the engine!!!!
The killer of the 'B' series is long fast runs. It was NEVER designed to go hours on end at high speeds. In the MGB it was improved with better crankcase breathing, but in the Farina, on English winding roads, there was no need.
The simple reason the 'B' series uses oil, is its technology. It is a typical early 1950's bit of engineering. By 1959 in the first Farina MG and Rileys, the engine was already 10 years out of date. Still in use in 1971 Farinas, and even later till 1980 in the MGB, its oil consumption was always going to look bad against more modern, SHORT STROKE engines. The breathing system is crude, it just blows out into the air outside. There is no proper crankcase controlled ventilation, so pressure builds up, and oil gets blown out. The faster it all reciprocates, ( spins,) the more oil gets blown out.
The very long three inch stroke gives the piston rings a rough time. They eventually wear, and are slopping in their groves. This leads to cronic "ring-pumping" of oil, up into the combustion chamber. Inlet guides wear, and the engine sucks its own oil into the inlet manifold. The last is VERY, VERY common, and can be partially cured by fitting later 1798cc MGB valve stem seals. Do not fit them to the exhaust guides or the valves will sieze, only fit to the inlets.
There is a lot of oil-splash in the sump, and the pistons get swamped with oil at high speeds, especially so if the bearings are worn and oil flow is even higher. Oil pressures are quite contentious, as the MG and Riley versions had a stronger oil pressure relief valve spring. These two models run on 75psi when cold, with a minimun pressure of 50 psi hot. The other three Farinas, the single carburetter Austin A60, Morris Oxford, and Wolseley 16/60, have 50 psi cold, and as low as 35psi hot. The only difference is that springs setting.
Anyone fitting a post 1964 MGB 1798cc , ( 18GB onwards,) engine will not fail to see the much better rear crankshaft seal, of neoprene, not the hit-and-miss reverse scroll-seal of the smaller engines. However, MGB's use oil as well once worn.
It is worthy of note, that to stop owners worrying, many modern cars fit only an oil pressure light. Looking at a guage gives cause to worry, but what if you find out that light only comes on a below just 7psi???