OK let me think out loud here for a second and see if we can figure this out.
I went to the Fel Pro site and found they gave you what felpro has listed as the correct gasket 7761-B-1. You got set HS-7761-B-2. The picture shows the gasket you have and you can see the number stamped on your gasket picture.
So now we have to wonder is that a felpro mistake or do they know something we are over looking. If it is a mistake I wonder how many have used this gasket in the past and are now posting here about over heating problems.
So just to get a better idea of the problem I looked at the gasket for the 134 motor 7632-B
and it looks more like what you need so at least felpro got it right. To bad the bore is differant and I do not know the details of that gasket or I MIGHT suggest using that gasket.
On the other hand if you look on this site or even the main Tisco parts site you will see that the 1/2 bolt gasket for the 134 and 172 is the same gasket. The gasket for the 7/16 is listed as a differant gasket for the 134 and 172 but that could be because Tisco sells a metal clad gasket for the 134 and a non-metallic gasket for the 172.
I wonder if contacting the felpro customer service and technical inquiries line at, 1-800-325-8886 would produce a answer to this problem.
Before I took anything else apart I would decide what path I was going to take. Most tractor sites sell a head gasket replacement set that only has the head gasket; valve cover; and manifold gasket. The next step up is a complete gasket set at more than twice the money. What you have is a head rebuild set. It is going to have some extra gaskets in it like the side cover. So if you go with another set you may not get a side cover gasket. But anyway that cover is just stuck on. They leak easy cause the cover gets bent so many gob it on with gasket sealer.
I do not know what path I would take. I would be very tempted to talk to felpro customer service and see if they would trade me the gasket for a 134 and try it.