Re: why so many 3.0 questions?
I said it was developed, not produced. the earliest I can find on a production run was late 58 as a side project to the 6cyl. was first used as a small industrial/truck engine and in the early chevyII. I have seen one in a 60 impala but could not confirm it was original. I think the iron duke was acually a 151 CID motor. shared nothing with the block/head of the 153. the 153 has been used extensivly as an industrial motor outside the states. south and central america is full of them on various industrial equipments. the 235 was replaced by a better 6 of the 194 version. took about 4 years to finnish it as the emphasis had shifted to the 265 and 283 and 348/409 development. some of this is my memory is fuzzy. in my twenties I did a lot of research on old engines cause I was working in a shop that specialized in old car restorations, did that for about 3 years. what a pain. was incredible how much iron was produced, some had such limited production runs that parts books wont list them anymore. the overhead cam 250 was one. its still hard to find parts for one. the iron duke moniker has popped in and out but is mostly refered to as the late seventies model of the 151 manufactured for the pontiac. however as a coperate engine it found use all over as a method of fuel economy. and that is why the 2.5,153and the later3.0,181 engines are so popular with marine today. they produce good power for their size and will perform well with minimal maint. there have been many changes over the years with intake/ex ports, pushrod lengths and rocker ratios. I think the earliest general production runs were about 1961 or so. AMC used them in the mail jeeps till sometime in the 70's. 820 jeep in Ft worth used to be a great sorce of heads,blocks and cranks for the old 110,120,135 and early 140 motors. I still see them in aircompressors and pumps all over. they will run for hundreds of hours at medium loads with no failures. so my dates may be off a bit but the fact that the 151 and the 153 share no common parts really is correct. both are listed in various places as a 2.5L but they are two different breeds. the funniest marinazation I ever saw was a guy used a 305CID GMC V6. did not work well at all.
. but in the late seventies to present due to hull size and fuel the 4 banger keeps plugging. however we are seeing more and more 4.3L in entry level boats. merc and volvo both wish the 3.0 would fade away but I doubt it will. however I do see the carbed version as being history soon. cant happen soon enough to suit me. the addition of the delco EST was about the best thing to happen so far. Marine power has a 3.0 that has TBI that is sweet. 180 HP and they can stand a 1.98 ratio 18ft galaxy on its head 
