Ben,
There is no longer a real "standard" from what I can see from the catalog- the SVT-410 HLF still appears to be a sealed enclosure like the classic SVT8x10" which has been on riders for about a half century, but also has an APT tweeter.
The neo- magnet PN-410 HLF is ported, so has is louder above Fb, but will "flap" if pushed hard below Fb, likely around the 3 dB down point. Can't tell from the specs if the SVT-410 HE is ported, I suspect not, it appears to be designed more as the top cabinet above a LF system.
My take would be a bassist looking for Ampeg would generally be looking for the sound of the SVT-410 HLF, and if they were picky, would have included a model number.
As far as heads, the classic SVT is all tube, sounds great, weighs a ton, and will require more upkeep than the solid state or hybrid units. If you buy one, the next 4 riders will ask for Eden, SWR, Hartke, and some unit no one has heard of before...
Art