Iv tried as well to keep exhaust fumes out and bring engine heat in, I even tried running a duct from engine compartment but,,,,,, that didn't work either lol
I've got a 78 316 with a cab and 18 Vanguard repower . I found a metal / rubber boot vent stack thingy at Menards , fit perfectly over the front grill . Clamped a 3"pvc elbow in it pointed up , reduced to 2" , up and back over the hood into a hinged metal panel on my Cozy cab .I hole sawed the panel and another short 90 pointed up at the front glass . Works great . I have run it 5 years and have had 0 problems with exhaust fumes . I have a stack on the muffler to make sure the exhaust gets away . Between this and the residual heat off engine and hydro it can be shirt sleeves on a sunny day .If I ever develop an exhaust leak it could be a problem , but I keep a very close eye on that . I can slip the pipe off over the hood and have it open in less than a minute to check oil and such .This was one of those experiments that actually worked quite well .