Were the batteries low when you made the switch ? I had the original alternator on my 4040 go out during planting. I swapped in a Delco that I have on a Oliver Super 77. When I overhauled it I converted over to 12 volts and went to the alternator It appeared to be the same just had to swap pulleys.  I put it on and had not gotten very far up the road until it got super hot and I could smell it. Thought there was something else wrong so I took it and the original in to be tested. The original was shot and it was cheaper to buy a reman than rebuild the old one. The one I swapped off the Oliver was still okay but did not have as high a rating. It was only like 60 amp and the one on the 4040 was like 75amps I think.  

 Repair guy said that with batteries being so low it was running at max capacity and was getting very hot. He said to put battery charger on batteries for several hours to get them back close to normal charge and then alternator could keep up with the load. Fortunately this happened one evening and I had already put the charger on the batteries overnight.