I live in a warm (sometimes too hot, like now) climate. We have very few, if any, days when the temperature drops below freezing. Lacking air conditioning on my 55 Tbird, if it's too hot or too cold for me, the car will remain in the garage. On the other hand, if your carburetor-equipped vehicle is your daily driver (unlikely for most of us), and you live in a cold climate, you probably should not block off the heat crossover. 

Heating the intake manifold went to the wayside with the advent of port fuel injection.  The heated manifolds were necessary with carburetors to keep the manifold warm to prevent the carburetor from icing up when the vehicles were driven at dew point or less ambient temperatures.

Lorena, Texas (South of Waco)

Has modern fuel made manifold exhaust heating totally unnecessary (electric choke/alum.manifold), even for northern/winter driving?

6 VOLTS/POS. GRD. NW INDIANA

I buy thin sheetmetal from Lowes that is .035" and cut with scissors to fit.  Works just fine, and is thin enough that the gasket seals without a bulge.  Joe-JDC

JDC

Thanks - it goes on tomorrow
Mike
'55 Glasstop 272ci 3sp O/D

I used an old license plate for mine. I put it between the gasket and the intake with a VERY thin layer of red RTV. Same size as the mounting surface. Worked great.

JDC - do you use an oversized piece of sheet metal that lays under the gasket or do you trim it to fit inside the hole in the gasket?  I haven't laid my gasket over my 2bbl intake yet to see what the fitment is like.
Thanks
Mike '55 Glasstop 272ci 3 sp O/D

Ted is probably on his way to Bonneville, or already there.   Torquing the intake, I would recommend starting from the center bolts and working your way out to the ends in a cris-cross pattern.  If your torque wrench will allow, start with 15# and then go to 20# and finally 23-25# in the same cris-cross pattern.  If your torque wrench is like mine, then hand tight the bolts and then torque to the lowest setting which is usually 20#, and then final of 23-25#.  I've used this on all my Y's and really haven't had an issue with gasket leaks or misalignments.  I do block the heat passage with a thin piece of steel and remove the embossed heat pad from the gasket before installations.  Joe-JDC

JDC

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Ted, do you recommend spiral or criss cross pattern when torqueing. Ive seen both in shop manual recommended on same part for different vehicles which really makes no sense to me. 
Seth