The FT58/2 were on Austin Princesses and Sheerlines
The one on the right labelled FT58 is actually an FT 57, which has a different closude under the front rim and hasa round instead of pointed back. This were also used on tractors , but not chromed in that case. The FT 58/2 had the pointed back and FT 58 type of screwclosure
One could say, remove the fin on top and fill the hole and replate the body and with some fiddling, use FT58 lenses to achieve the MK IV style lamp.
the FT 58s seem to cost more than FT 57s. FT57s appear regularly on ebay uk.