They are differant.  The 351 heads (D00Z and C90Z)
have slightly bigger valves than the 302 heads of the
same era.  That's good.  Port sizes are also slightly
bigger; and that's good.
   But the chambers are a little bigger than most 302
heads, and that's kinda bad.  You'll lose some
compression.  Depending on the pistons you're using, it
might not matter.
   In later years, 302 and 351 heads are the same

The specs on your 70 351W heads are somethinlike this:

PN C900Z-6049F, used on 69 and 70 engines
CHamber vol 56.3-59.7
Valve size:  I-1.84, E-1.54,
Port size: I- 1.76x1.94, Exh- .96x1.24

PN D00Z-6049C, also used in 69 and 70 engines
CHamber vol 58.9-61.9
Valve size:  I-1.84, E-1.54,
Port size: I- 1.76x1.94, Exh- .96x1.24

The only differance in the 70 heads vs. the 69 is the
chamber size.  Lowering compression for emissions.

If you give me the part numbers for your 302 heads, I
might be able to give you thise specs.  My book only
goes up to 1970.  (it's an old book).