Mounting a 5J blade onto a 1939 D2 3J

trade 4 a 3j blade. u do know the difference between a 3j and 5j?

I would show it to a welder.

It would be some work, but should be able to cut it down to size.

Not only do you need to cut the frame down but the blade also. With the narrower track base the wider blade will tend to steer you more than you steering it due to the leverage of the resistance caused by the width.
Trying to move the mounts out will be a breaking/bending point on your Track Frames.

Hi, JDP.
Unless my aging eyes deceive me, that appears to be a straight blade, NOT an angling blade. If I have not been deceived by mine peepers, you only need to cut the width difference from the middle of the blade and weld the remaining 2 parts together again. Note that I said, "ONLY". It'll wanna be a pretty good welding job - done with due regard to cutting edge bolt hole spacing, proper alignment,, properly prepped Vee-ed weld faces, the right electrodes/mig wire/gas, etc..

Bolting a section of cutting edge across the joint will help with alignment and also to hold it in alignment while welding.

I agree all of Drujinin's points except 'cutting the frame' if it IS a straight blade.

Just my 0.02.

The difference between 3J/4U D2 (40" gauge) and 5J/5U D2 (50" gauge) SHOULD be 10" in width. Of course there is always the possiblilty of worn treack pivot shaft bushings etc throwing things off.

In addition, if you have the option, you probably would like to have large idlers on the tracks to take out some of the "rocking horse" tendency that a normal early D2 has. While this is an advantage for drawbar work, making it easier to turn the tractor while pulling implements, it makes dozing more of a challenge.

Thanks guys, the blade is in fact a straight blade, so cutting the width of the blade 10" appears to be the best solution.

Thanks!
I didn't blow up the photo's this morning to see the blade.
Just know what typically needs to be done to get the job done!
Yes, In this case picking a spot to cut out is probably the toughest!
Would probably do some measuring across the Cutting Edge bolts to see if 10" could be found easily.