Just my two cents. I don't know why felpro doesn't include those. Being new to Corvettes I haven't had to do that job. I also have a 90 TPI. Usually if the shop manual is silent on the issue of gasket maker I wouldn't use it. Why? Unless stated the sealants and gasket makers are not recommended. If you use a little too much and it oozes out most of those materials will foul the O2 sensors.
Felpro is usually high quality. I was a Ford guy for 35 years and the mechanics at the dealer always recommended Felpro. Our local machine shop, in busineess over 50 years only recommends Felpro.
I guess you just buy the other two pieces.
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If it isn't broke, I haven't fixed it yet....