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Hi Robby, I much prefer the original underhood style muffler for my '42B. I used an above-the-hood muffler for many years and always had a problem with rain water getting into the exhaust manifold and through an open exhaust valve, even with a rain cap installed on the muffler outlet. My B is always outside. The rain would follow down the muffler inlet pipe and through the tight clearance where the inlet pipe enters the exhaust manifold. It is my understand that the later OEM AC through-the-hood mufflers took care of that problem by having the muffler casing enshroud that area. The cheap Stanley above-the-hood replacement mufflers do not have that feature. In addition, in order to use the later AC OEM style, you need to have the two attaching holes in the later exhaust manifolds. According to my parts book, this later AC muffler began use in 1951 (ser #B114400), so if you have your original manifold, you might not be able that use it anyway. If that's the case, you are left with either an above-the-hood or an under-the-hood style one as best I can tell. If you only have one hole in your manifold for the muffler attaching bolt, you should have had the underhood style muffler originally. When I returned to the original underhood style muffler (OEM AC $$$), I was also concerned about the heat affecting my then fresh paint on the hood. I decided, as a precaution, to use a heat shield product by Eastwood on the underside of the hood. You can see the edges of that insulation in this photo: 
I didn't use it over the entire hood, only in areas around the muffler and extending a few inches out. I have not had any problem with heat affecting the paint in several years and I use my B all the time in the summer. The riser section on the muffler outlet is not part of the muffler. The stock muffler outlet pipe stops only two or three inches above the hood. I added an extension to get the exhaust point a little father up off the hood in an attempt to prevent exhaust fumes from being carried into my face. You can see the extent of that extension here. The problem of getting water into the exhaust manifold has disappeared since I went back to the underhood muffler, even with no rain cap on the exhaust riser. I also have some unique (I think) AC-B info on my website here if you are interested.  Rod
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