Along with DP/Dummy conversions, 66's can also be converted to fire the 21mm sub cal rocket.
Not to piss on anyone's parade, but the manufacture of these homemade 'Ukranian connons' (as we called em when I was a kid) can be dangerous, and in some places they are illegal. Example, powerful enough to launch a softball right through a car door, not the glass, but the metal!
Users beware.
Go to alocal gunshow or two, and spent launchers can be purchased legally at a variery of prices, depending on the version and condition.
Cheers,
Wes