Spitfire overdrive question

[Adam Frankel <frankel@uhunix.uhcc.Hawaii.Edu>]

Hello spit gurus,
  I have a 1980 1500 car.  There is a 1974 Mk IV with overdrive for sale,
cheap.  My question is, can I (somewhat easily) take the J-type overdrive,
mount and driveshaft from the Mk IV and bolt them into the 1500?  IF so,
could someone send tips and hints and so forth.  Finally, how much does a
J-type overdrive drop the revs?  (Can't seem to find it in my references
materials).  
  Thanks in advance,
adam