Here is my experience with fumes/heating in my bay.
I bought it back in August this year and there was a really bad smell of fumes/petrol. I disconnected the heat exchangers until I could find the problem. It turns out that there were several reasons why I was getting the fumes/petrol smell.
First problem was that there were rust holes in my heat exchangers (in the exhaust pipe running through the centre of them). This allowed exhaust fumes to get into the heat exchangers and be ducted into the cab!
Second problem was that the rubber seals around my engine bay were almost non-existant, they were so old, they had cracked up and there wasn't much of them left. This allowed lots of dirty "engine-smelling" hot air to come up into the engine bay from underneath the engine and the exhaust. There were also some holes in the tinware which contributed to this effect as well.
Third problem was that the twin Weber carbs on the engine were leaking petrol all over the place...major source of petrol smell!! The petrol had dripped out of the carbs, right onto the heat exchangers...hey presto nice intense petrol smell in the cab!
Fourth problem was that the oil breather pipe beside the oil filler hole was dripping out oil. The oil filler pipe itself was leaking oil from underneath it (turns out there was a gasket missing altogether)
To solve the problems, I got rid of the Webers (they're for sale if anyone wants em!), got a stock inlet manifold and a single stock carb. I got new aftermarket heat exchangers (they'll do til I can find good original ones), new stainless exhaust system. I installed new engine bay rubber seals (took the engine out to do this) and plated up any unwanted holes in the tinware. I thoroughly sprayed the engine with gunk spray to degrease it and generally clean it up. I took off the oil filler tube and put a paper gasket underneath it to stop the leak.
Thats my experiences anyway. Before I fixed the problems, I made sure to have a carbon monoxide alarm sitting on the dashboard. It never went off so I presume that the majority of the smell was from raw petrol and not carbon monoxide from the exhaust.
