Hi John.
If you do need a new alternator, why not use a standard (very inexpensive) automotive one with a suitable output.
It will not have a sense wire to worry about as it will just use the voltage at the +ve terminal to regulate.
Tho' if you have 'splitting diodes' you'll lose at least 1/2 a volt (not good), but you can replace them with 'Sterling's' low loss equivalent to get the voltage back up to 14.5v+.
The cost of the alternator and Sterling's smart little box will cost a lot less than buying Volvo's outrageously expensive one. ( which will just be the car one with a sense wire fitted) ..................Bill