Help: Radio in a Series Land Rover

Hi.

I've got an 1980 Series III Land Rover which at speed is a tad noisy.
Its previous owner had graced it with a rather nasty Goodmans Radio
Casette and 2 dual cone pioneer speakers mounted in the driver and
passenger doors.

When stationary or with the engine off - the system sounds absolutely
fine (I'm no audiophile).

However, at speed, I need to turn the radio up a fair way to hear
anything. The treble shines through, the base vanishes and what I can
hear really isn't worth listening to.

So my question is this: Should I put up with no radio and admit it
that no system turned up loud will drown out engine noise..

...or Would repositioning of the speakers most likely help or would a
better radio / speakers be a wise investment?

Many thanks in advance for your help,

M