Answer: 321

Solution:

The integer parts must be equal: $8a + b = 12b + b,$ so $8a = 12b,$ that is $2a = 3b.$ Since $a$ and $b$ are nonzero base-eight digits (at most $7$), the only options are $(a, b) = (3, 2)$ and $(6, 4).$

The fractional parts must also match: $\frac{c}{8} + \frac{d}{64} = \frac{b}{12} + \frac{a}{144},$ i.e. $\frac{8c + d}{64} = \frac{12b + a}{144}.$ For $(a, b) = (6, 4)$ the right side is $\frac{54}{144} = \frac{24}{64},$ forcing $8c + d = 24,$ which has no solution with both digits nonzero and less than $8.$ For $(a, b) = (3, 2)$ the right side is $\frac{27}{144} = \frac{12}{64},$ so $8c + d = 12,$ giving $c = 1$ and $d = 4.$

Indeed $32.14_{\text{eight}} = 22.23_{\text{twelve}},$ and the requested number $\underline{a}\,\underline{b}\,\underline{c}$ is $321.$