Hi there Malcolm,
If you are going to change the outer axle flange seals, have a good look at the rear bearing seals. Could be prudent to replace them as well. As for the bearings protruding out past the bearing housing, that should not happen with the correct numbered bearing. A70 and A90 did not have the small section O rings that are often associated with modern seal kits purchased, which are fitted around the groove created by the rounded lip of the outer bearing diameter. For 50 years, all I have I have done when replacing the axle flange gasket is.if the seal is still OK, wash it clean with turps, dry, then apply some non hardening gasket sealer.
With the new rear seal, when I did not have my press, I used a flat bit of steel placed over it, gently tapping it in, with the outer studs on hardwood timber.
With new bearings, never hit the bearing with a hammer, always use a brass dolly to tap it back into place, only applying tapping the bearing on the outer case.
As for the main differential pinion seal, BEFORE you remove the nut, the tension of which is crucial, and on A70/90 diffs, this is only around 6~8 INCH LBS FORCE, ensuring that excessive crush is not applied to the two tapered rollers on the pinion shaft. This does not include any drag created by the lip of the seal on the tail shaft hub.I suspect that it would be similar to an A40, but you need to check in your manual.
Before starting, spray the thread with some “nut release agent” to loosen any binding, giving it time to travel into the nut. After peeling back the lock tab washer that secures on one of the nut flats, then using your brass dolly, gently tap on each of the nut flats, progressively going around in a circular motion.
Then, starting at 2 inch lbs, check the force required to LOOSEN the nut. At this setting, the trip on the tension wrench should activate immediately when applied. Then increase by 1 inch lb settings, until the nut cracks loose, which should not be more than 10 inch lbs. Note the setting.
Before refitting the nut and tightening, thoroughly clean the splines on the pinion and tail shaft hub, and both the pinion and nut threads. Make sure the lock tab nut washer and mating surfaces are both smooth and even, and apply a smear of grease to them. Also apply a smear of grease around the surface where the seal seats on the tail shaft hub. If needed, adjust the spline tabs on the lock tab washer for a better fit using long nose plyers, then fit it and the nut. I then increase the increase the release setting by 0.5 inch lbs, and tighten the nut. Secure the washer tab against one of the nut flats.
The reason for the grease is to ensure that the least resistance is felt by the nut. Even when doing my own rear assembly on the bench a few months ago, even the pressure of the seal had an affect.
I have used the above a couple of times over the years, when doing an “in car” diff seal replacement. Hope it assists in some small way.
All the best-Peter
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