Just curious...  did the heads or pistons get changed durring the
rebuild?  If so it may be that the compression ratio has been changed. 
In fact depending on exactly which parts were changed your compression
could be changed radically.  I'm right now re-doing my '81 because I got
greedy and tried to get away with 8:1.  even very cautious driving
brought the oil temp sky high ( 310 degrees in the pan for you squemish)
At first I thought it was a mixture problem and that the heat was from
running lean.  In the process of trying to get the fuel better I managed
to overheat the heads and drop a valve seat.  Shame too as these were my
favorite 914 heads.  There's more to the story as this is a stroked
motor with FI and yes, before you all beat me up, I knew better than to
let it get that  hot.  Greed is a terrible thing.  Anyway, If they are
high compression heads or pistons that came out of a 914, or you changed
the stroke, even an oil cooler will not save you. BT,DT.  This week mine
is going back to 7:1 with a little more conservative dish in the
pistons. Hopefully that will give redeem me so I can go camping again. 
If you are sure that none of these parts were substutited for the
originals then I'm not sure what to tell you. Good luck and be sure not
to push it until you find the problem or you WILL be buying new parts.
Mark