my new 604 cabinets I'm building.

[voice of the theater]

I would wait to cut the ports until you hear from GM and others here as far as their recommended size and location of the ports. I don't know much about building cabinets, but I think there's a reason that all of the Altecs I've ever seen had ports in the front of the cabinets, not in the back. Also, the page you're referencing (in your post number 30 of this thread) shows a picture of an 846A Valencia. Again, I'm far from an expert on DIY cabinets, but if that picture is any indication of the date/year of the "Altec bulletin" you're using as a reference then it's a very old reference (from the 60's) and I know that the cabinets Altec used back then were tuned much higher than later Altec cabinets like the Model 19 cabinets. I think by the later 70's Altec had a much better "handle" on cabinet tuning as far as how to get really deep bass out of a cabinet. I wouldn't use the port size that Altec recommended in the 60's if you want to get deep bass (more modern "hi fi" tuning) out of those cabinets. As I mentioned before, I'd wait and get recommendations from GM and others here (regarding port size/location) based on your exact cabinet dimensions and 604's that you're using (or in lieu of that, find a much more modern source/reference to achieve a more appropriate/modern cabinet tuning that will allow significantly deeper bass)......

Wow--those are beautiful cabinets--nice job!! Have you/how are you going to determine the port size/location/cabinet tuning?

That's why I asked you this question earlier in this thread. I suspect the problem you're having with the AS 101 cabinets is that they're not tuned for 604's (and someone apparently also failed in their attempt at DBR tuning with the "shelves" they installed in the cabs). I think these new cabinets will be much better for your 604's IF "appropriately" tuned/ported. You're at a crucial step right now that will "make or break" the success of this project IMHO.....