i might also add a couple of points
if you are intent on useing the delco units:
you should be able to bypass the regulator interally and bring out the one or possibly two wires that deliver power to the rotor, and use an external regulator for charging and via a switch use the reostat for welding.
a purpose built regulator or marine charge controller would be the much preferred means of battery charging control as either example would allow for much higher and faster charge rates to your battery bank.
there are a couple of manufactures of charge controllers that can handle two alternator fields (rotors) that have multistep charging regimes, ie. bulk, absorption, float, and equalizing set points, along with temp sensors for the battery to allow for temp compensation. these controllers are specifically designed to charge deep cycle battery banks in the fastest and most economical manner, (lower engine run time).
the delco regulator does not have that capability, and while able to deliver 100 amps will taper back drastically very quickly, far before the batteries require. this means much longer run times. these regulators are basically designed for charging starting batteries which deliver short bursts at high amperage, and charge a bit differently than deep cycles.
do a search on marine charge controllers, those folks lead the pack on alternator controllers for deep cycle charging.
also why do you want two 100 amps? is it for charging capacity or welding?
100 amps can do quite a bit of welding if you keep the rod diameter small, like 3/32"
such as 6013 for out of position and 7018 for down hill and flat work.
and finally if you are not locked into the use of the delco units, then take a look at the prestolite/leece neville units, of 140 amps.
these are externally piggyback regulated units, larger in diameter, heavier built units, that run about 150 bucks US new , without any core charge.
also they can be had sometimes for nothing from truck shops as there is no core charge, usually all they need is new brushes and a set of brgs to put them back into operation.
they will charge at 90 amps at engine idle of around 1300 rpm at the alternator, and jump up to full rated power at around 3000 rpm.
if you like i will see if i can find my link to these units and post it.
bob g