The Delco 12SI was the replacement for the Delco 10SI. The 12SI was typically a higher amp. 78-94 amps was what they came in. The 12SI and 10SI will both bolt up in place of the 10DN that you are currently running. Only difference was that on some of the 12SI alternators they had a slick mounting hole on the adjusting ear and internal parts of course. If your going to upgrade to an internally regulated alternator I would suggest going with a self exciting one wire Delco. Its a lot cleaner, neater wiring set up. I can help you out with what you need but you will need to Private message me on this site for more info.
Thanks
Ken