[FFR428]

With keeping the date codes in mind the 65 might be better smog exempt wise. Plus the C4 heads are lowrisers which I've always liked. The D2 heads are the same casting as the earlier C8-H' MR's. The D2's have induction hardened seats for unleaded. BUT some of the D3 block castings have nodular maincaps unlike the grey iron caps the C4 block most likely has. You can see the "ladybugs, warts or bumps" as they are known as on the maincaps. You should also see a brinnel indentation on the side of one or more caps. Tough call either way. I'd drill bit test both blocks to see which has the better cyl wall cores. The D3 block might have thicker wall cores possibly. I've also seen lots of C4 block casting that got the crossbolt bosses also. Some of these have had thick walls also. Guess the main point I'm trying to make is you'll need to look inside to make your decision. Both could be very good choices. JMO,

G.