OK, found some specs. All '73-76 429's and 460's were 8:1 except the '74 275 horse 460, at 8.8:1. The earlier performance 429's had from 10.5 to 11.7.
With both having the same ratio, the 460 must have dished pistons, so would end up with the same ratio as your 429 has now.
If you are going to rebuild it anyway, the 460 conversion might pay off. I wouldn't tear down a perfectly good engine for a 30 cube gain, though.
That 8.8 comp. version in '74 probably had flat-tops, those might be worth looking for.