If you want someone else to work on your radio you might check with
Gary Tayman in rec.antiques.radio+phono
he does these conversions on a regular basis, and is a frequent poster
over there.

Also If you are in Canada, you might contact Larry Wood
@woodradios.com I think he has gone into doing something similar as
well.

In consumer radio restoration , replacing the innards of a tube radio
with a bunch of IC's is kind of frowned upon, as most of us strive to
restore the radios instead.
What I am saying is that you do have a choice, if the car is stock ,
personally I wouldn't go this route unless I couldnt' fix the
orrigional radio for some reason, but it is a personal choice. I have
an old volvo with an AM radio that was a transistor set, and my choice
was to plug a FM tuner into the antenna , which the radio recieves on
AM at a set frequency. That way I still can have the stock radio in
place and tuck the FM unit away . If the car is old enough to have
tubes, it will also have a vibrator and solid state vibrators are
available. Either Gary or Larry might be able to give you the option
of restoring the set for you as well if that is what you want. any old
radio will probably need to be re-capped and alligned to work right.

Phil