Denis, fyi, I have stamping on the front of my block, but I've interpreted this as meaning the date that machining was performed. My block casting is July 2, but machined on July 12 (so has the "8G12B" stamping there). But Kachi-san's information helps reinforcing an obsession I have, that many of the 302 engines used in Mangusta were made the first week of July, 1968. Btw, 8ma1046 had "September 1969" printed as the build date (on the bulkhead sticker...I've only seen this otherwise on 8ma936). This is why I guessed a ~November '69 manufacturing date. My heads and manifold are all the same week. My intake manifold is exactly as '1088 (cast 8G5), with stamped DeT engine number 302/209. You know, I have a distributor from a Mangusta in the mid-8ma600# that is also marked 8G2--Ford production seems to have been a lot tighter on inventory control in the 60's than I would have assumed !
Tachi-san, I think the only valuable part about the "hi po" heads were because of the installation of guide-plates and adjustable rockers necessary for the mechanical camshaft. The standard 235hp engine (shipped with all the 302s) used a low performance hydraulic camshaft, so anyone wanting more performance would modify the heads so they could use a higher lift camshaft. This is easy for a machine shop to modify.
If your car was built for the US market, it would have had the smog pump (and the bell housing will have a pedestal to mount it, that Euro cars did not have). The heads were the "smog" type and had ports for the air injection. But my guess is only about 5% or 10% of Mangustas still have these (!) I am curious is DeTomaso shipped any Euro cars with the smog pump, and I'd speculate that 289s were used for Europe so that DeT could avoid warehousing the non-smog variant 302....!
Tachi-san, I completely agree with Denis, you are very lucky to have your original intake manifold, most (or at least, many) Mangustas have lost theirs and this is the only really unique component to the engine. Everything else is easy to change or repair, and (unlike old Corvettes or Mustangs, where tens and hundreds of thousands of cars were made) this kind of detail is really not so important in the DeTomaso world.