The answer is in the first part of this article from:

http://patriot.net/~jonroq/Text/R3_R4eng.txt

R3 Option:  Special production order from Paxton (Granatelli
brothers).
304.5 CID, 9.5-1 compression, Dual belt driven Paxton supercharger (8
in.
crank pulley, 4 in. blower pulley), special cam, heads, pistons, tube
connecting rods, cast exhaust headers, non-sealed AFB carb in a large
cast
pressure box. This car also had solid inner suspension bushings for
tighter
handling.   Only 9 were sold  as production orders, however there are
cars in
which these engines were installed afterwards by owners, etc.  There
was an
interesting option offered  with these, called a Carb-u-meter, which
was
installed in the dash console.  This included a vacuum guage and 2
carburator
adjustment screws to fine tune the engine while driving.  There were
only 9
made, all 64's, the first was R5089.  They seldom change hands, but we
hear
$30,000 to $50,000 figures mentioned.  However, Paxton Products had
several of
these blueprinted, hand-assembled R3 engines left over when Studebaker
ceased
production.  They sold them retail for about $1660 for a couple of
years.
There are probably 20 or so factory-built R3 engines running around in
various
Avanti, Hawk and Lark bodies.  There are probably another 50 or so
engines
which have been built up to R3 specs and use the R3-style carb box.
   Nine Production R3 built & delivered - serial number r5089
turquoise 4 spd,
r5237 black 4 spd,r5394 white4 spd,r5532 turq 4 spd r5546 gold 4
spd,r5593
grey auto,r5625 black auto, r5642 white auto,r5643 white auto.  The
last 2
cars were in fact the last Avantis built by Studebaker in Nov 1963. Joe
Erdelac
owned the last one and it is in a museum collection after he donated
it.  At
some point in my collection of stuff, I have seen the original
locations
(Destinations) of shipping for these cars, that i,s the dealer
location,
R5089 is in the basement of Joliet Studebaker where it's been sitting
apart
for over 20 years. The owner has acquired nearly another complete car
in NOS
parts to restore the R3, but has not done anything.  He offered the car
to me
two years ago, than backed out when his son objected to the sale. (BTW,
it was
built with a 4:88 rear !) The following are the original locations of
the r-3
Avantis:  ( R5642 - Moline IL) ( R5089 - Downers Grove, IL) ( R5593 -
Yuma,
AZ) ( R5237 - Seattle, WA) ( R5394 - Kingston, PA) ( R5546 - Ft.
Wayne,
IN) ( R5643 -  Jackson, MI) ( R5625 - Toledo, OH ) ( R5532 - Vauxhall,
NJ )
 The one Daytona (64vi9585) was sent to Albany NY