Yes, the alternator does need a warning light, the spade terminal on back of the alternator is called exciter, as it excites it to charge. You can have a bulb wired in line under the dash or under the bonnet if you don't want it in the dash, but without a bulb lighting up, the regulator won't act. A sparky could also prob put a resister in the wiring to do the same job, if you want to check that out.
70amp alternator is fine unless you have a lot of electronic gear, stereo, heap of lights etc in the back. Most of these cars originally had 35 or 40 amp alternator unless factory a/con, & then it was 55 amp