Do we agree that the head on my 68 looks like a GYT and the cylinder looks like stock? Not sure how I will put it back…stock heads for sale seem rare. About half the pics I see of 68s have this head vs. a stock head. Single vertical plug. Does it make much difference in performance to simply add a GYT head and leave the stock cylinder? Out of my comfort zone doing mods on these old bikes.

That appears to be an original '68 cylinder head, not a GYT head. A GYT head has the center plug, plus another hole machined towards the rear of the center plug. I have put GYT heads on several stock cylinders, no ill effects, but to be honest I've noticed zero positive effects either. The GYT head produces just slightly higher compression, but very likely not something you'd notice.
And yes, that cylinder appears to be a stock Enduro barrel as well.
On Ebay the '68 head generally sells for $150, the GYT head $150 as well, the stock DT1 head can be found as low as $30.

Thanks HouseofEnduro…I value your input and knowledge.  On Dealer brochures and my original 68 1st edition rider’s manual they show the original head as one plug at an angle out the side. No second plug hole. I’m just starting my journey on a faithful restoration of the old girl. I’ll test my patience on this one I can tell.

Not to confuse the topic but here’s my NOS ‘68 head… single hole angled to the right side. 

  

I'm just going by what I've read but my understanding is both the 68 standard head and 68 GYT head both only had one plug hole.  Angled on the standard head and straight up on the GYT version.  (Early manual said early GYT plug was centered and something like "inline with the bore axis")

This was also recently confirmed by Enduronut in this post:  yamaha-enduros.com/index.php/forums/gene...frame-numbers#137491

It was 1969 when Yamaha added an extra hole as a feature to install a compression release or second plug. 

 

MarkT’s understanding is how I understand it as well. I’ll probably search for the angled one hole head but as I am trying to exercise patience on this build I will keep the one hole vertical head for now. The journey continues. I knew the 68 would require lots of input from folks with way more experience than me! Please share what you know!