rod(nh) or anyone

Rust pits are a PITA to deal with. Sandblasting is the best way to start. You could always try the Extend but whatever you do, if you want a nice smooth, glossy surface, you will need to apply a pourable bondo and or lacquer spot putty, probably in multiple applications to your satisfaction, with lots of sanding in between. A final sand with 400 grit paper or fine ScotchBrite is needed before topcoat. No easy fix here.

If you are going to grind all rust away, I wouldn't use Extend at all. Extend works best when there is a continuous, tightly adhering layer of rust to react with. That's why the instructions say to remove loose rust only, usually with a wire brush.

If you have clean steel (no rust) you can put bondo directly on the steel, after it is ruffed up some by sanding (or grinding). I prefer instead to apply epoxy primer first, scuff it with a ScotchBrite pad and then apply the bondo. A matter of preference.

I want to emphasize that I would only use Extend where there is serious rusting that would be difficult or impractical to completely remove by grinding or sandblasting. Light rusting such as might occur by humidity exposure or being left out in the rain for a few days is better handled with a phosphoric acid treatment and etching process such as DuPont 5717S/5718S; or possibly a combination of sanding and such acid treatment. There are many products out there that claim of "solving" the problems of dealing with rusty surfaces. The best fix is to sandblast to bright metal and epoxy prime immediately. Anything less than that is a compromise. My opinion, of course. Others may wish to describe what works best for them in similar situations.

That's the Extend stuff in rattle can. I have tried the spray-on but much prefer the brush-on/roll-on version. I couldn't seem to get a high enough film build to really do the job with the very fine spray from the can. In any event, it doesn't need to be "sealed" at all. Once it completely reacts with any remaining rust and turns fully black, it can be exposed to the weather. The time to turn black is very dependent on temperature - the higher the temperature, the faster the reaction. I have had a test section of the brush-on Extend on a severely rusted and pitted dump body for over three years now...two coats and nothing on top...outside all the time. No sign of any rust showing through. I have used it (roll-on to minimize brush marks) on a gas tank that I didn't want to sandblast the bottom of because I was afraid of blasting right through some very tender metal on the tank. I topcoated that with epoxy, then a surfacer and finally a topcoat. If you have a uniform coating of the Extend, you probably can forget the epoxy but I think you definitely would need a surfacer on the tin if you want the smoothest, most glossy finish. I used an epoxy because I did not have a uniform base, the bottom of the tank being treated with Extend and the rest of it basically bare or sandblasted.

If you do decide to prime over it, be sure to follow the Extend spec sheet for dry time. It says a minimum of 24 hours. However, if you are below 70 deg F, I would personally wait several days prior to putting anything on top of it. If you use epoxy on top, be aware that after the epoxy time window, the epoxy has to be scuff sanded and usually recoated to get best adhesion of the topcoat. It sounds like you would be in such a situation. No such window exists for any of the surfacers that I am familiar with so if you have a uniform Extend surface and don't need a bare metal primer, you could just leave it or apply a surfacer now and wait until you are ready for the topcoat.

Wet sanding? I don't do any wet sanding. I just prefer doing all mine dry. If you are going to use a surfacer, I would just scuff sand the Extend with a coarse ScotchBrite pad, apply the surfacer and sand (now or later) prior to your topcoat.

I can't help you with a DuPont color number but do have a reference to PPG numbers for Massey Harris red and yellow. Maybe you could cross them over at your DuPont dealer. In any event, I do not trust numbers and crossovers for the old tractor colors. You best bet, once you have a possibility, is to buy a quart (minimum purchase for a shop-mixed paint) to verify the proper shade prior to spending a lot and possibly being disappointed with the result.

Rod