Ok guys, I've done a clip (yes, a mere phone clip) and some pics.
My non vented has date-code GU18; 18th of July, 1986. The vented one has KT17 (17th of October, 1985).
I did some seperate speaker A/B tests, switching the inputs from one to the other. At first I had the vented one up top (Marshall 1966A cab, diagonal 2x12). More 'vintage-y' and a tad more middy and smooth. Definitely close to what a G12-65 sounds like, but with more 'kerrang'.
In fact, it sounds like how I wanted the new Creamback G12M-65's to sound! But those were a stiff mess. Sold them quickly.
The non-vented T75 sounded close, but maybe a bit more punchy and a tad more aggressive.
Just to be sure that the cab position wasn't an influence, I swapped the position of the two; now with the non-vented up top. This also made it more middy, but its punchiness remained and the vented one remained the smoother of the two.
Now for the Captain Plan... ehrm.... Punchitā¢ mix, it was time to hook both vented ones up. See images.
Like
@DanTravis62 said, if you're only used to the 90's and later versions, you'd be surprised how 'woody' these old ones sound. Like borderline Greenback-with-more-lows-and-punch-woodiness.
Sure, I had an actual Pulsonic cone '72 Rola Greenback and that was pure classic rock tone...very Paul Kossoff. But since I play more metal than classic rock, I sold it, but got a pair of pre-Rola 30W 55Hz cone Greenbacks in return. Pretty damn tasty too.
Anyway...
And this is how they sound together (quickest way was to record it with my little Engl Ironball, since it's late here and I didn't want to get my neighbours...aroused.
Clip: