I don't know what brand 4 into 2 you have. The ones I have, used the original headers that were cut off of the stock 4 into 4 mufflers. The 4 into 2 setup had each muffler accept two head pipes. The Y was made into the muffler. It actually slipped on. The Y being sized for the stock head pipes.
Don't know where to find such a thing, anymore. I bought mine in 1975, cheap, about $75 as I recall. JCWhitney used to sell them, too.
Let us know if you find "slip-ons" for the four head pipes. Maybe a muffler shop can adapt something.
The stock pipes may be more expensive than your value system. But, they look good, and are still far cheaper than a new bike. And work much better than just about anything cobbled together to "get by". Of course, if the bike isn't worth the parts cost to make it work properly, than what's the point?
Cheers,