Originally Posted by: detective ...it may make a bit of sense about the C20's and C30's having a similar engine to the HK 327 as I'm pretty sure they were marketed out here as well ?? Would they have been available in around that timeframe ?
No. We basically only ever got 292 6cyl engines in C20-C60 and K20 trucks and only from 1975 to about 1980. The very last of these we got 350's in (around 1979) but only in C20 and C30 and only because emissions requirements were introduced during 1978 for trucks, and the 292's couldn't comply.
The story of the type 2 327 is a very complicated thing, but essentially it existed in the form it did due to a number of contributing factors:
The previous supply engine plant for HK 327 engines (Tonawanda) ceased 327 production at the end of 1968 GM model year production (model year is September-August, with production for the model year August-July).
There was no passenger 4BBL 327 in 1969 model year, only the 210hp 327 (small 2BBL as per 307) and 235hp 327 (large 2BBL as per 1969 L65 350). Both of these 2BBL engines appear to wear 3927185 69cc heads for 9:1 compression. I'm not certain of their origins and who built them but I know Flint built some (possibly all) Impala 235hp 327 and logically McKinnon built the 210hp engines as small 2BBL engines is all they were building until sometime in 1969 calendar year. My guess is Tonawanda built no 327 engines after the start of July 1968.
It makes sense then that McKinnon Industries supplied the last of the HK 327's completed in the latter part of 1968 (which we know they did), they'd simply have used the same bottom end from the 210hp engines (same cam, same pistons etc), and logically they imported the 4BBL intake from the nearest other plant (Tonawanda) as McKinnon were 6 months away from 4BBL engines. The only fly in this ointment is the 210hp 327 was dropped from Camaro and all other 1969 model Chevrolet and even Canadian GM vehicles by around October 1968 (replaced by 307). Exactly what else McKinnon were building that wore the 3927188 75cc heads is unclear - almost all 350's used 1.94/1.5 valves, and 307's used 69cc heads (they'd be about 8.25:1 with 75cc heads). The 188 heads aren't imported as they are McKinnon cast. There was one 350 2BBL C40-C50 truck engine in 1969 that used 1.72/1.5 valve heads, it was 8.0:1 with dished pistons and would have used 75cc heads, so it is possible the 188 heads belonged to these if McKinnon Industries built this engine. If so the 2nd type HK 327 engine is truly a mismatch of parts put together solely for GMH.
As to the reason for the mismatched exhaust manifolds, the only reason will be is that McKinnon produced the LH one (their driver's side) for some application but the other side (our driver's side) was obviously no longer produced by them, so they had to get one from Tonawanda.