As I noted earlier, I tow my 60 behind a large motorhome. To tow a 40 with a 80 is asking for issues and problems not related to mechanics of the drive train.
When using a tow bar, or even towing a trailer, it bad practice to use a tow vehicle of the same or similar weight as the towed vehicle. In this case 80 pulling a 40, way too close in weight.
Another issue is brakes. The 80 has marginal brakes from what I understand (never driven one!?) and now you are basically doubling the braked load! Not good!
By law(California) and good practice, any towed load over 1500 lbs must have brakes and emergency brake away brakes. Something to think about also.
I have never had problems towing my 60, and you see thousands of jeeps and other 2 and 4 wheel drive vehicles being towed via tow bars with no problems. Common sense prevails, use it and few issues arise, don't use it at your own risk.
Doug