Why does valve train weight matter? The heavier the combined valve train weight is, the stronger the springs must be, with a given cam profile, to achieve a given RPM. The more spring load there is, the faster the cam lobes and lifters are worn. So keep the valve train light.
Flathead V-8 lifters may be adjustable or fixed. Some of the weights I’ve seen are
45-52 grams. Hollow stock non-adjustable lifter. There are at least three types of these.
83 grams. Production hollow adjustable lifter.
103 grams. Modern Johnston adjustable, solid, with oblong lots on the sides.
118 grams. TRW made adjustable lifters for Ford.
143 grams. So far the heaviest I’ve found; a 1953 part number solid lifter.
As you can see, the big difference, especially percentage wise, is going from any fixed to any adjustable lifter. If you think that weight is critical at the RPM you expect to run, you should adjust your lifters by grinding, just like Henry did.
If you are not ready to adjust by grinding, then use adjustable lifters. Use lifters that have slots or holes in the sides. The lifters in the Flathead V-8 are all “solid” by type. This means that they are not hydraulic. Some are hollow, however, to reduce weight. The slots or holes in the sides allow you to 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.
To avoid using a lifter wrench, drill a hole in the lifter boss 5/32” diameter, as low as practical. Debur the lifter bore where the drilled hole enters. Then, after 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.
The mechanism that keeps the adjusting screw from turning in the lifter body is clever. On most Johnson style lifters 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 screw threads quite effectively keeps the adjusting screw from turning in the lifter body without undue wear.
There is another style that is used in some adjustable lifters. It is much less common than the one described above, in my experience. The bottom end is slit up the sides. The bottom end is spread open a bit, possibly after the adjusting screw is assembled in the lifter body. They also have a necked down area. 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, possibly due to the cutting action of the edges of the slits. It is very difficult to be able to successfully get one of these screws back in once it is 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 a plastic locking compound, like “Locktite”. 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 the locking fluid after each adjustment.
There is a current production adjustable lifter where the hex turns the entire top of the lifter. The adjusting threads have a plastic material injected into the center cavity and out into the threads in four places. These appear to be working well in service.
Hardness should be Rockwell C scale mid-50’s on the bottom of the lifter. You can check this with a file on the bottom corner. If the lifter is hard enough, it should not file readily – the file should “skate” on the material without cutting.