According to this DSA article from the Duodecimal Bulletin:
It seems the Dwiggins "dec" was a particular stylistic implementation of the roman numeral X and the Dwiggins "lev" was a particular stylistic implementation of an upside down '3'. Now Unicode doesn't mandate stylistic choices (i.e. whether the top of a '3' digit should be flat or rounded or whether an 'X' has certain curved characteristics leaving such stylistic decisions to the typeface) but does contain a "Roman Numeral Ten" and "Turned Digit 3" in the "Number Forms" block of Unicode in the BMP (i.e. U2169 and U218B) both of which seem would be appropriate code points for the Dwiggins numerals when the numerals are viewed as a stylistic typeface implementation of a roman numeral X and upside down 3. Besides being in the BMP when doing a basic character sort the roman numeral X comes before the upside down 3. Even if they don't make the same stylistic choice sometimes fonts make the roman numeral 'X' slightly more number like than the roman letter 'X' and seeing other roman numeral X's and upside down 3's probably won't cause mass confusion in a dozenal context.
The Roman numerals code points seem to have been included in Unicode to support some legacy CJK fonts and it seems Unicode doesn't recommend them for composing actual Roman numerals (they seem to recommend to instead use the latin letters I, V, X, C, L) so there might not be too much conflict with actual Roman numerals in text (and if there was the author could switch to an appropriate font in the relevant sections).
Hence to display the "Dwiggins" numerals within the current Unicode standard all we would need is a 'Dwiggins' Unicode font/typeface that implements (part of) the Number Forms Unicode block while making the same stylistic typeface choices as Dwiggins did when designing his version of a roman numeral 'X' and upside down '3'.