Any advice on 727 install?

generally, if you are using a trans cooler, you route the line through the radiator first, then through the cooler then the return back to the trans (the front is the hot fluid/pressure the rear is the return)

so it's probably best to go from trans front line >>> radiator >>> out from radiator >>> cooler >>> out from cooler >>> rear line on trans

you can just bypass the radiator but at that point the cooler has to do ALL of the cooling not just part of the cooling

does the old torque converter have any balance weights on it? or if it's a flywheel that came out does it have any holes drilled out to balance it? if so you might have a cast crank. i think the original '71's were forged. so you should be ok. the front balancer should have an eccentric & lettering that says "cast crank only" if it's the externally balanced type