That's the problem, the '48 four speed is non-synchro. She needs double-clutching every shift, or, when you learn your engine speeds in each gear, clutchless shifting. There aren't any automatics that'll fit without a lot of work, an engine/trans swap would be better. Or learn double clutching. Thats where you shift from low to neutral, let up the clutch and gas, press the clutch again when the engine has slowed everything down, and go for second. Repeat for third and fourth. Clutchless shifting accomplishes the same thing, but you don't declutch, just let off the gas enough to slip it into neutral, then when the engine hits the right RPM for the next gear, click 'er in. Very satisfying when mastered, and amazes your friends no end! Catch a ride with a trucker someday, and watch him close.