Cantom, your expecations are WAY unrealistic. On a short run, the cost would be more like $100+ and still FAR cheaper than an original would cost on e-bay.

Also, it would have sprue marks and need to be polished. you would have to have the checkering pressed into the top of the ears after the part is made. Also, it will need to be finish milled to fit the barrel properly.

Forget about punched in markings showing up at all. Luckily, if you are anal about it, a set of letter stamps are cheap at princess auto and the LB mark is just an L super-imposed over a B. Then you need to have it blued.

This is NOT an inexpensive undertaking.

Consider that the repro SMLE Mk1 rear handguards with wax cast sight pretector is about $250 US and though it comes with an inlet piece of wood, the guard is a much less complicated casting than the sight ears you are looking for.

The cheapest solution is to have an original No.4 LB regular sight protector altered to duplicate the waisted one. It will involve some milling and welding but will be much easier than casting a repro IMHO.