Who drives their classic in winter? If I start my engine in winter months I want it to run for awhile.
For these reasons I blocked off the exhaust crossover in the intake manifold and 'gutted' my heat riser valve. At the time, I was assembling the engine.
I simply cut the middle out of the heat riser with a torch. The outsides still look the same (although they cannot move). Of course, there is a 'blank spacer' for sale but I simply made my own from the original piece. The insides are smooth with no holes. No restriction, no exhaust escape.
I have heard from many dozens of owners who knew their gas mileage was bad, power wasn't quite there and they had terrible heat problems. Yep, all due to a stuck-shut heat riser valve. A few used a small hammer to knock the valve open. They simply hit their stuck valve until it rotated into the open position, then left it that way.
BTW, Bulldozer engines, 430 MELs, never used a heat riser valve. - Dave