did they ever put 427's in '70 chevelles?

No,the only non COPO car to receive the 427 was the 'vette.I'm not sure but the Yenko S/C Chevelle got a swap out for the 427 but that was in 69'.As well the 69' Camaro got a 427 but it was a COPO (corporate office production order,extremely rare!) But in 70' the Chevelle came either a 396,an LS5 454 or the LS6 454
Hope this answers your questions