The gearbox ECU is programmed not to lock the torque converter until a specified temperature has been reached but it's quite a low temperature. I had my 80 just running aux coolers without the in rad cooler due to a blockage and it took at bit longer to warm up. I would leave the rad cooler in circuit given the choice but I don't think you need to worry about over cooling without it unless you're in very cold conditions. I haven't priced this but I'd look to fit an OEM aux cooler, from an 80 or 100, in front of the coolant radiator, with a 10" fan on it. 80's work their box very hard, it would be hard to be OTT in keeping them cool if you visit hot places. Having low gear manual lock up and using it goes a long way towards keeping them cool.