There are GM NOS ( 3 ) intake manifold sleeves on ebay right now
$12.00..........they are in excellent near mint condition .
Fits 1950 to 1962 ALL ( ex.216 )
Go to ebay & in the search box.......type........3835506
They have the correct factory specs - correct thickness - the correct spring action & the correct depth & the correct I.D. & O.D. when closed
and are made in the U.S. A.
Certainly better then out of spec homemade .
So , why buy made in china fake repro's .
Here's a GM NOS set that sold on ebay last month for $7.00 .
GM NOS for less then chinese fake junk .