The EQ heads will bolt right on to the Magnum block. Retaining the Magnum rocker arm arrangement is no problem, but you'll have to check pushrod length no matter which lifter setup you run, since Magnum blocks have a slightly shorter deck height.
You say you want EFI but you mention dual plane M1 intake. Should we assume this means one of the throttle body setups like Holley Sniper, not a full factory Magnum style EFI?
Post a picture of both M1 intakes you have, so everyone knows for sure what your options are.
If you keep the same camshaft, you may be leaving a lot on the table, in terms of performance. You'd basically be running the same overall setup with more cubic inches, and a little better driveability from the EFI.
