The lifters in our Flathead V8's are all "solid" by type. That means that they are not hydraulic.
They may be adjustable or fixed. Weights are 45-52 grams for the hollow stock non-adjustable lifters. There are at least three types of these. The old production hollow Johnson lifters weigh in the 83 gram range; the French hollow adjustables weigh about 93 grams. The current production Johnson lifters are not hollow, but they do have the oblong slots in the sides -- they weigh about 103 grams. When TRW made adjustable lifters for Flathead, they came in at 118 grams, the heaviest I've found.
As you can see, the big difference, especially percentage wise, is going from any fixed to any adjustable lifter. If you think that lifter weight is critical at the RPM you expect to run, you ought to adjust your valves like Henry did, by grinding.
If you are not ready to adjust by grinding, then use adjustable lifters. Use lifters that have slots or holes in the sides. This is so that you can hold them without using the lifter wrenches at the top. It is difficult enough to get the thin 7/16" tappet wrench between the spring retainer and the lifter boss, without trying to also fit in a lifter wrench.
Drill a hole in the lifter bosses 5/32" diameter, as low as practical. Don't forget to deburr the lifter bore where the drilled hole enters. Then, after final cleaning when you are setting the valve lash, put a 5/32" allen wrench into the lifter slot or hole through the drilled hole in the lifter boss.
Why an allen wrench? It is made of tough steel and the adjusting torque will not shear it. (Don't use a nail). The allen wrench also has a handle to pull it back out easily.
What is the mechanism that keeps the adjusting screw from turning in the lifter body? On most Johnsons, there are two sections of thread, separated by a necked down area. The pitch indexing of the two sections is not the same. This stretches the necked down area. The resulting tension on the threads quite effectively keeps the adjusting screw from turning in the lifter body.
Illustration #1
There is another style that is used in some adjustable lifters. It is much less common than the necked down version, in my experience.
Illustration #2
The bottom end is slit up the sides. They also have a necked down area. The bottom end is spread open a bit, possibly after the adjusting screw is assembled in the lifter body. The springiness of the steel screw segments against the lifter body threads provides the self locking action. These do not seem to last as long as the first type. I have never been able to successfully get one of these screws back in once it was completely removed.
I have never seen a flathead Ford adjustable lifter with a free adjusting screw and lock nut. I have seen an adjustable flathead Ford lifter that has a free adjusting screw where the locking mechanism is "Loctite" or similar. The breakaway torque is over 45 ft-lbs. After it is turned out and back in, the breakaway is under 12 in-lbs, or under one ft-lb. This is not satisfactory unless you can clean the threads and reapply a thread locking fluid after each adjustment.
What should you look for if you are thinking about having your adjustable lifters resurfaced?
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The bottoms should be surfaced with a 96" radius, convex. The bottom should not be flat or cone shaped.
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The finish should be fairly smooth but does not need to be polished.
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The adjusting screw surface should be refinished with a smaller convex radius, about 36". This is because the adjusting screw orbits as it turns. If it is surfaced flat, it will only meet the valve tip squarely once per revolution.
Resurfacing is the only way I know to get serviceable hollow adjustable lifters -- unless you get lucky and find some NORS.