They are the Canadian SBC design head for 1968 model year (9/67 to 8/68) only, for applications that required a small valve, small port 69cc head. They are 1.72/1.5” valve, 69cc chamber, 142cc intake, 59cc exhaust.
Direct fit on Chevrolet engines, and identical design and part number to 3917290 which is a Tonawanda Chevrolet head. Functionally identical to 3927185 which is the 1969 (accessory holes) version of the head. There may be another.
Used in 1969 on 307 and possibly 327 210hp (2BBL) which was the standard V8 in Camaro. Mostly fitted to Canadian and export cars such as Pontiac, Studebaker, Holden plus both Canadian assembled Chevrolet and afaik also sent into the USA for fitment to Chevrolet vehicles. Might have been used in Ramsay Marine applications. Used in Australia in HK and HT and may have been supplied by GMH for use in local boat applications.
There may have been some high torque truck 327 applications for the 032 head too, not sure if McKinnon built such engines.

Edited by user Wednesday, 5 May 2021 7:14:40 PM(UTC)  | Reason: Not specified

It is the head that was on all HK-HT 307. Good for a standard 307. Work far better with a 4BBL intake and Quadrajet plus dual exhaust. Very limiting much more than that due to small intake valves and ports.
There are far better heads out there. Some of the later 305HO heads are good, have 1.84” intakes and small chambers plus decent ports, just have to be careful with head gaskets (you want 3.875” bore gaskets). From memory 601 casting.
If you have a 60 thou bore any of the old fuelies with 1.94” intakes should be good. The first Corvette alloys from the mid 80’s (L98 I think the engine was) are 58cc and 1.94 intakes which would be good for a 307 plus 60 with reasonable cam overlap as static compression would be over 10:1.
There are small bore aftermarket alloy heads available too.

I assumed it was a typo as there is no 30xxxxx SBC design head casting number.