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I think the "186" heads were used by Flint and the "041" heads were used by Tonawanda. 

All factory big valve heads got the chamber mod around the intake valve at a minimum.  Glad to see you have at least one head that also has exhaust valve un-shrouding that looks to be original.

Who ever did the machine work on the ones you have for sale didn't cut the valve reliefs on the small valve head core.  They really should have cut them if you want them to match.  Need to also examine the throats behind the valves to see if they bowl hogged them open when they added big valves to the one head (originally small valve).  Maybe you can have that done locally?  Hard sell without that. They will not flow the same. 


One head looks like it has steam holes added between the bores?

Do these cuts at the exhaust valve look factory?

I have a set of very nice "186" heads that look to be completely original and correct except the combustion chambers have the valve un-shrouding machine work on the intake AND exhaust valve walls of the chambers.  Not a deep cut by the exhaust valves but looks to be factory.  No port work mods at all.  The valves are the special GM swirl polished type so I think they are original to the heads.  Have any of you seen this exhaust valve wall cuts before? 

charts are for service, not assembly line.  Best guess explanation I can come up with.  No need to stock all those springs. Close enough was good enough.

Eaton Detroit is who I would call.

Anything before February 26th '69 would work. 

Distributor stamping is December 20th of '68 350/300 with manual transmission.... Looks good to me.

It probably had "041" heads on it originally.  Should not be too difficult to find some.  Carb is a lot harder to find and if you do find one it would not be cheap.

Large journal 327.  That crank flange looks like a 3.25" stroke and the block is a 4" bore.

The pad shape is right for a '69 and the casting number is right for a '69.  The Flint plant assembly stamp is not right for a car.  The implied assembly date of March 26th, 1969 would line up with the short time period this casting was used but the rest of the assembly stamp has too many digits as the "8" does not belong there and the 2 letter suffix does not match up with any typical car application.  Casting date has not been shown yet but I would expect it to be around March something of '69.  If there is a VIN derivative on the pad by the oil filter we might be able to pin it down but without that info, we are just spitballing in the dark.

If there is no VIN derivative there, this blocks original configuration will never be determined.  No reason to worry about it.  It would be just another engine block.

..Or just go with the '69 and up damper and timing tab.  GM makes an inexpensive bolt-on tab for the '69 and up 8" damper. #12342011 about $14 or so.

Responding to the above post - Cast number on the hub is not the number to use as the hub itself will be commonly used in other non-Camaro applications.  The stamped "2222" number on the outside face of your damper is the number to reference.  Long version of the number is "6272222".  That part is a "69 and up timing mark. The photo does not look like a '68 production line damper.  I don't know how to read that date code.

The keyway on the SBC crankshafts are in line with the #1 and #6 crankshaft throw so that does not vary.  The timing mark on the damper varies and needs to match with the timing tab you are using so they are a set on any application.  The damper mark and tab zero are in different locations for different chassis applications due to needing to see the timing marks in service. the factory '68 damper/cover timing mark should be lined up 2 degrees off the crankshaft keyway centerline.

You can try to find a 50+ year old production line damper to try to use or just a common aftermarket replacement damper.  There are also reproductions now of the '69 and up "2222" part, but I have no experience with those.  I would not go that route personally as aftermarket replacement dampers are a better value.

As long as the damper has a sharpie mark where the zero on the tab lines up when the engine is at true top dead center you are golden.

a radiator cap designed for a coolant recovery system used on a non-recovery system maybe?   Just spit balling here.  Check your cap.

Test it with an aftermarket replacement fan clutch.  About $30 or so from Rock Auto. 

Trick Flow Specialties makes a nice aluminum version of the "double hump" factory heads.  They have the same casting marks so they look stock but flow way better than any ported factory head. They have them either with or without the accessory bolt holes in the ends to keep the "look" right depending on the year of the car. This would be the place to use them. 

Roller cams are nice too but the cost increase for all the required parts/upgrades is around $1000 over a flat tappet build. A stroker mod would be more cost effective.  Maybe do both.