FWIW I've found that the exhaust temperature under load once my 261 gets "up on the cam" 2700RPM and up) to be pretty high. I attribute that to early opening exhaust valve. On motorcycle engines I'm familiar with that contributes to more exhaust noise too. On my truck it pretty much burned the guts out of a FlowMaster muffler. The 848 head that came with the 261 from a bondyard in Wis. had valve rotators on it. I used my recently rebuilt head without the rotators but now I wish I'd made the swap. My Ispro pyrometer indicates 1200 to 1350 deg. F under load -- for hours on end.

1951 3800 1-ton
"Earning its keep from the get-go"
In the DITY Gallery
1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.