I plan to plug hot slot holes with steel plugs and remove heat riser flapper (doesn't get too cold here in southern California). i will be leaving the riser body in place for that original look.
Do I still need to use the stainless steel baffle underneath the gasket?
Also, the guy that rebuilt my quadrajet included what looks to be a spacer with the rebuild. It's about 1/4" thick and seems to be made of plastic. Do I need this as well?
You must have removed the headers you mentioned earlier if you're going to use the heat riser valve; there's no way to use the heat riser valve with headers.
The stainless baffle goes under the carb on an L-35, on top of the gasket, as shown in the Assembly Manual.