Random question.. intake exhaust crossover with headers ?

Since you don't drive the car in the coldest winter months I'd block the exhaust crossover and not worry about it. I blocked the crossover on the 360 in my '72 D200 pickup with an Edelbrock Performer intake manifold and I'm glad I did, running an Edelbrock carb with a 1" phenolic spacer it still occasionally percolates the gas in the bowls slightly. It probably takes a bit longer for the intake to warm up but even on the coldest winter days I've started it up and was on the road within 5 minutes.

I imagine back in the days before ethanol-blended fuel (which is also 'designed' for fuel injected engines) the heat crossover was pretty important. But modern E10 gas vaporizes so quickly and easily it's not a big deal to keep the intake hot anymore and it'll likely cause more bad than good. Only time I've experienced issues was running an Air-Gap intake on the last 360 in my Duster in 25 degrees (F) or less on the freeway; I would sometimes get carb icing with that setup. Now I'm running the same carb (Street Demon) still with no heat crossover but a non-Air-Gap RPM intake and the residual heat from the oil splash on the underside of the intake as well as heat transfer from the aluminum heads, it now runs very consistently and I have zero issues in super cold temps.