S-P 3 upgrade

I have had an AR SP-3 for almost 40 years and continue to enjoy it.  Am considering the official upgrade which is only done by AR.  A less extensive service by the only AR certified tech in my area costs nearly as much,o I am not interested in that option.  Is there anyone out there who has had the SP-3 upgrade done, and what is your opinion about the outcome?  Grateful for any thoughts!