You're lucky, keep all the units-IPC means International Projector Corp. (SIMPLEX) wheh they bought enough Altec or other speaker manufacturers would label to suit.
IPC part No LU1004. So speaker could be Jensen, Stephens,Lansing,RCA etc. Don't discard but carry out more investigation.The composite horn I had was just like yours, only difference is colour, yours either painted or original grey removed.Does it have the original wooden horn sled?Your system is P.M types with Altec N800 X/over.Did the HF unit have a gasket,I see the horn flange cracked at both mounting holes, be careful.