Questions about heater core and switches

[70 c10 rook]

I've been educaTing myself(or powering up my brain like I tell my son)on this forum and let me tell you there is endless info and I learn every time I'm on here. So my questions are where might the best place to get a new heater core or should I have mine repaired the hoses that come thru the firewall are loose and broken where they attach to the core itself and does anybody sell the rubber gasket that seals the unit against the firewall and also there's a switch attached to the back of one of the plastic pieces is that availableI don't have a clue what it's called. This is a 1970 a/c cab all original so while I have it tore apart I'd like to replace the 45 yr old part. Thanks for any help