Not sure this clears it up completely but here's the Wikipedia entry on the subject: http://en.wikipedia.org/wiki/GM_Iron_Duke_engine The first example showed up in 1977 in the Astre, a Pontiac Vega clone so it was presumably rear drive. First transverse installation appears to have been in the '84 Fiero followed a slew of applications in front driver GM product in 1985. Original was supposedly manufactured by Pontiac Division. Early engines were pretty weak sisters at 90HP or less and 123lb.ft. of torque. Substantial changes were made in 1982 and the engine was rechristened the Tech IV but power remained the same that year but rose to 98HP by 1988. TechIV has the same bellhousing pattern as the 2.8 V6. 2.5 was superseded in 1994 in pickups by a new 2.2 liter motor with a HP bump to about 120.
I had a 62 ChevyII with the 4 banger, 3 speed and a posi rear end. A guy gave it to me and I drove it all one winter. I had another one in a boat. It was rebuilt and a sweet runner (120 merc). I had a hard time giving that boat away. And FWIW, the 1/2 of a 460 marine engine would be much larger than any Chevy 4 banger at 230 cid.
"Are the front wheel drive 151s from the early 80's the same as the earlier rear drive iron dukes? these should still be plentiful" All the front wheel drive 151s use the smaller bolt pattern like the 60 degree V6s. I'm pretty sure the last year for the old style V8 bell pattern was 1980. There were actually two blocks being made in 1979 and 1980. One for the rear drive Monza and its clones and the other introduced, in 1979 &1/2, on the new X cars: Citation, etc. I believe all the 151 blocks used in later rear drive cars & trucks were the smaller V6 pattern.
The FWD engines are much weaker. They have a very light duty crank with small counterweights. It really is not a bunch better than a model A crank except for using 5 main bearings. The FWD blocks are weaker, The heads don't flow well at higher revs and are prone to cracking as the deck surface is thiiiiin. The 89 and up S10, Astro vav and mail trucks have a better block, better crank and cross flow head. They also use the smaller bell housing and flywheel, which woks well in a small roadster. The S10 head is still no high performance part, but it should work well enough. The block is also configured for distributor location in the normal forward position and in the rear position unique to the crossflow engines. A cam designed for the S10 has distributor drive gears at both locations, too. Some 235/250 6 cylinder parts will fit or can be easily adapted. I installed a harmonic balancer on mine frome a 250 as the tech4 has none. The water pump wouldn't exchange as the water jacket is deepr or the casting is thicker on the 6. The impeller hits the cylinder!
A good source for parts is http://www.bmara.com/cl***ified.htm HRM did an articl in '60's about reversing oil flow so the mains got it first. A good idea if racing.
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