Welcome to diyAudio. Looking forward to your project. I am a lifelong Altec fan. A divided Onken style cabinet might just fit the bill.
Thank you for your response, are you thinking a sealed upper chamber for the 604 and ported lower chamber for the 416? That’s the way the 6041 was built I think, I really can’t find any actual plans for the 6041, just one image that is in an Asian script. I like the look of the Onken cabinets much better than a 6041 box.
If it were me I would do the 416 in an Onken style as the bottom part of the cabinet and maybe a little fooling around with the 'airiness' of the 604 by poking some holes in the back like in the first pic. Mine, as you see it, has the CSS woofer for support and it is active. Consider going active with your system as well. The cost of passive parts hardly makes sense and active gives you that much better control. I cut the 604's off at about 100 Hz.
