Howdy Back Peashooter:
Your original thread inquery was "Will the later heads be bolt ons to your '68 engine." The basic answers was "Yes, but". You said your goal was increase performance and cleaning up oil contamination of your spark plugs.
Then Dude suggests that you keep you '68 head and modify it. All this confused you and you asked for more pros and cons. So let's start from the beginning.
Your 68 200 engine stock is down size on performance when compared to earlier 200s because FoMoCo reduce the carb cfm size, from 185 to 150cfm, to improve mileage and reduce emissions, but they added a better distributor with both centrifugal and real vacuum advance with both advance and retard capabilities, again for better emission numbers. So, given that, then what.
Your oil contaminated spark plugs are likely due to bad valve guide seals. Or possibly ring seal. Best way to know is to do a compression check. If the cylinder pressures are good, then you can likely conclude that the problem is the valve guide seals. It is possible to replace the seals without removing the cylinder head. You can buy seals separately for about $25. They come in a valve job gasket kit for about $60. The Kit includes a head gasket as well as all other gasket to replace a head.
If you were to remove and redo your '68 head and upgrade as Dude suggests it will require a valve job gasket set. The machining to do a performance valve job will include a surface mill cut to true the mating surface of the head. The head gasket in the gasket kit will be a thicker composite type which will reduce compression ratio unless the head is milled more that the truing surface cut to maintain stock CR. Upgrades to come up to a D7 head would be a set of 1.75" intake valves and having hardened valve seats installed. There goes any savings by staying with your '68 head. The remaining difference is that the intake tract volume of the '68 head is 1100ccs. The later heads come in at 1,345ccs. There is no reasonable way to make up for that difference.
The cons with the later head is that the carb mounting adapter, linkage, fuel lines and air cleaners are different. This problem requires some problem solving, but addresses the biggest performance short coming of a stock '68 200- the downsized carb. There are several solutions, as retaining your stock, downsized carb is one of them. The other is an additional mill cut to reduce chamber volume, not a big deal.
So, all things considered, keeping and reconditioning your stock head is reasonable, but only if you intend to remain mostly stock. If you do decide to go this route consider limiting you upgrades to milling .025" to compensate for the thicker replacement head gasket and then specify to the machinist that you want at least a three angle seat cut, along with a 30 degree back cut on the intake valve. The recon head will be assembled with new valve guide seals, mostly likely solving the spark plug problem. I would choose that route only if I planned to use stock exhaust manifold and stock carb.
IF I were planning to improve performance beyond the above, then I would go for the late model head. I'd find a donor Fairmont or Granada at the recycle yard and go from there. I might grab the Dura Spark II ignition system from the same donor, but that's another story. Most recycle yard heads can be had for less than $100. I've never paid more than $50. Next take it to your machinist for disassembly, cleaning and inspection, then the machining. Remember that you are driving your car the whole time. Once the new head is ready, unbolt the old and bolt on the new. You are now ready for improved exhaust and a bigger carb (?). A typical valve job in my area is about $200 on a six cylinder head. You will have to check on prices in your area. That price will be the same for either head, except for the added cost of installing hardened seats in the '68 head.
So, after all that, you will be money and performance ahead with a late model head. And the head will support other future upgrades. And you were able to drive your car while the prep to the head was being done. Equals less down time.
Back to the beginning! Start with a cylinder pressure check and go from there.
So, more to think about. What do you think?
Adios, David
