Firstly do not cut your Hood being 70 it may still have the original hood , 1 year only .
I have a friend with a flat hood in Airdrie we saved as a possible shaker hood if needed it may be available .
budget 5k to do a shaker conversion , this includes a new hood & all the parts to make it work , I doubt you would save any $$ converting a flat hood .
The Shaker hood on a Chall was a very rare option in 70 I do not have the numbers handy but 200 for the whole year or so . Second the Shaker was available as an option on Challengers , I know of a factory 383 4 bbl , so yes you could get 383, 440, 440+6 or Hemi & possibly 340 with a shaker hood .
The Shaker is restrictive , the openings are small & tend to starve out 6 pack & Hemi engines , We did a whole dyno tune on a SS Hemi Cuda & tuned in a bunch of power then installed the shaker & had to retune way back down again , in SS you have to run the grilles in the scoop so we couldn't even leave those out .
The suppliers I am aware of are Roseville , talk to Dave or Paul , they are awesome to deal with & offer discounts to members here .
Also Gene Gregory in Alhambra ?
& Ben Snobar