I recall a few Toyota engines of that period with loose valve seats which would certainly cause the vacuum to bounce. Find the misfiring cylinder and run a leakdown test.
As for that old Toyota running with points, you might check for an igniter attached to the coil or near it. If you find an igniter the points rarely need replacement or service because they only carry enough current to trigger the transistorized igniter. and can outlast the engine.
edit; on second thought the 1974 seems to have the inline 6 engine with a cast iron cylinder head which is unlikely to use pressed in valve seats.The inline 6 was somewhat of a clone of an early GMC engine.