Ok, time for clarity......
"Change to electronic regulator." I'm sure you meant "Change to 70 and later" but the fact is WHAT IS PICTURED is already electronic, it is in fact a modern day replacement for the mechanical, but it IS electronic
"VR has nothing to do with alternator." Well kind of but not exactly. SOME alternators DRAW MORE FIELD CURRENT.
You can easily "rig" your new 90 A up with a battery, clip leads, and your multimeter and check the field draw. Simply hook one field terminal to the battery, then through the multimeter in "current" and then the other field terminal back to the battery. If it does not draw more than about 4-5 amps, your present regulator is probably just fine.
Even the old "heavy duty" Mopar alternators specified a heavy duty regulator........
Remember these?
So, what do you do?
Post a link to the part no you bought, so we can see what it "is." It is likely an "isolated field" often wrongly called "dual field." That is, two field terminals. If so, you can add one wire and convert to the 70 / later VR. Buy a good brand. Even an original Mopar from a junk yard is probably better than the "current crop."
Somebody, "I forget who" was advertising VRs that can handle more field current
Here we go. These guys "are claiming" their unit handles up to 10A of field current
http://store.alternatorparts.com/partnoc8313.aspx
Your new alternator MUST have two field terminals, this is essentially for 70/ later units