I pulled my head to replace exhaust valves and had it machined while it was off. The shop that did the machining said they removed more than expected, but that I will be fine using a stock thickness head gasket. That does not seem to be the case. At higher RPM the piston is hitting the spark plugs and flattening the plug gap.

I don't have the time to start this all over again and replace the the gasket with a thicker one, but it doesn't seem like there is another way out of this. The labor cost to have a shop do this would be too close to the value of the car, so I don't think that is an option.

Do I have any other options? Are there plugs slightly shorter that could be used?

Since this isn't my daily driver I'm really trying to find a way to not tear this apart again. Has anyone had any experience with spark plug indexing washers? This wouldn't be their intended purpose, but they might do the trick here.

Spark-Plug-Indexing-Washers-14mm-Tapered-Seat-30-Pk

 

You can get a spark plug that is 2mm shorter than the one shown here. That would work