I got one of the aluminum 440 source housings to put on the 440. I will need to replace the heater core in the car later on down the road when i get more time. On the factory housing i had 2 pipe plus in the heater hose outlet holes. On this aluminum housing, one of the holes is bigger and im having a hard time finding the right pipe plug to screw in it. I found one that is 1/2 but the threads dont go all the way up so the head bottoms out on the housing and just starts digging into the aluminum when tightening it..I need the type that gets tight when there is still thread showing. The smaller hole is fine as its the same smaller size as the original housing and the pipe plug works fine in it.

A regular plumbing 1/2 NPT pipe plug is bottoming out? EDIT IF this is a permanent plugging you might coat the plug with JBweld to get it to seal. Does it appear the hole (which is slightly tapered which pipe threads are) was tapped a bit too deep?) MORE EDIT trying to visualize this, if you shorten the pipe plug would it appear that it would tighten up/seal before the bottom of the plug hit the bottom of the tapped hole?

can you get a pic to post ? one of the plug, and one of the plug with the "head bottomed" on the housing.
also, what material are the plugs made of ? brass is best [in my opinion], but if using steel or stainless, a good sealer is a must, especially when it comes time to remove them.

didnt chrysler run 1/2 and 5/8 hose at one time?------made it really hard to source the correct hose.....

You need a plug like this one that has an allen head and no shoulder. If you can't find one at hardware store boat dealers sometimes have them.

If

My 71 Hemi has these.

This what you need?

https://www.manciniracing.com/mahehoni19la.html one 1/2" and one 5/8" heater hose

or

https://www.manciniracing.com/mahehoni19.html both 5/8" heater hoses

Got it straightened out..The brass plug i bought did NOT have NPT threads to it..it was threaded with regular threads. I found the correct plug today and it worked fine. Thanks for the help guys!