How about a decal?
https://www.ebay.com/itm/Decal-for-...-235-embossed-valve-cover-/282430890856.You can also go to a shop or online website that does computer generated vinyl decals.
If you can get the scaling correct (lay a scale beside the script), you can take a picture of your valve cover and have one made.
They are in the business to make several at a time so the pricing is higher initially.
People who do my hand professionally, like license plate lettering, use an oil based Sharpie and/or Craft Smart chisel tip paint pen.
There are videos on the internet.
