get the newer style donor tank and cut out all the holes (sending unit, and two check valves) and weld them onto your original tank. that way the tank will still fit and you will have all the provisions and required parts for the newer style system. this assumes you replace the sending unit opening you have now. the pro to this is that you wont have to add the pressure sensor as its built into the newer sending style sending unit. the con is that you will have to remove the old sending unit which will render your gauge useless since the newer style cant run your gauge...

TWO options:

1) you ADD the newer style opening to have both of the sending units in the tank, which will probably be very difficult due to the baffles inside for fuel slosh.

OR

2) you go ahead and replace the opening with the newer style and the add your old float (just the float) inside somehow in order to run your old fuel gauge.

i know what i just said sounds really confusing but it makes sence if you read it a few times. lol anyway, thats kinda what i did and is how i would do it if i did another cali swap again. im running two floats in my tank. and while i was in there, i added a second pump for my future mods. but in doing that, i had to drill holes and add wires. doesnt seem like a big deal until you have to find a way to seal it up!! and it has to stay sealed and be COMPLETELY sealed for the evap test to pass... hence my point of just welding all the provisions in your tank that way everything just plugs right in and seals like it should PLUS it will look factory to the ref which is what you want. just know though that if you go with option 2, you will still need to get two wires in the tank and seal it which is why option 1 is nicer but harder to do.... if you still go with option 2, make life easy and fork up the cash for this...http://www.racetronix.biz/itemdesc.asp?ic=BCWS-001&Tp= trying to dick around sealing up your own holes is not worth it. trust me!! pick that up, looks factory and allows two extra wires for a second pump if you wish.

my only concern about welding the tank is the inner coating to protect against rust. never dealt with that before so idk anything about it.

i would post pics of what i did but i didnt take any. lol sorry. but dont ask what i did tho cuz im lucky i passed with the way i have it (i almost didnt pass because of it) and im sure your ref will say no. go with anything i posted above and im sure you will be just fine. def not a walk in the park tho...