I'm sorry but am not following your suggestions.
"Rubber plugs" ... can you elaborate for what, where, why, etc.
"Weld patch" ... same question ... although won't be welding due to not having equipment.
"Core" ... what core ... and what would 'bracket' be for?
Again, all I'm trying to do is install a non a/c heater box where an a/c heater used to be ...
and re-install the dash ...
and need some ideas on how to get the heater to line up with the air tubes mounted on the underside of the dash ...
while at the same time marking screw hole locations on the new 'plug' in the cowl area to ultimately secure the heater box ...
and then cut out the access opening in the 'plug' where the motor will be inserted to be attached to the upper part of the heater box.
Thanks for the input.
IIRC you can use rubber plugs, or if you are ambitious weld in a patch. As for fitting the core, you may have to make a bracket or track one down.