Alright so I'm buying a Vox Ac4tv amp. The output rating is 16 ohms. It's a 4 watt tube amp that cranks pretty nicely. I happened upon a very vintage speaker cabinet. I ended up getting this cabinet for free (an old local electrician hand made it). The speaker inside is a 12" Jensen SG-222, which is 8 ohms.

Apparently this speaker is very nice, but doesn't handle lows too well. The cabinet it is inside of can fit another 8" speaker, possibly a 10".

If I wire in series a modern 8" woofer that has an impedance rating of 8 ohms, that will make the total impendence 16 ohms which will match my amp, correct?

Also, will I need any sort of crossover in the cab so that it directs the lows to the woofer without capping out the Jensen 12"?

Is there anything that I'm not considering that would keep this from working? Should I just sell the speaker and use modern speakers in this cab?

Any suggestions for an affordable 8" woofer that is 8 ohms?

Any help at all is appreciated.
Yes wiring the two speakers in series will get you a total of 16ohms, and you could run them both just like that or go for crossovers if you really wanted, however when push comes to shove if your thinking about putting in crossovers and another speaker in their, itd probably be just as cost effective to put a new modern single 12" in there. The paper in that old speaker is probably dry and brittle, id bet the same for its rubber surround, you'd hate to spend all that time and effort with the 8" and a crossover just to blow the old 12"

The thing is...
That speaker is Hi-Fi. Not really good for guitar.

That speaker is what you would find in a PA stystem. Or home theater system if Jenses does that.
..I was watching my death.
It's intended for mainly clean indie music, but will be used with a punch sometimes. Here's my band's first sample
The Evening

Vocals are kind of rough there and fixed now. So don't mind them :p

I'll do measurements today and find out what possible speaker arrangement could be used. I'm going to be using it for gigging though; small gigs, but still.

Could someone recommend me a setup if i take out the Jensen and build my own in that cab?
Guitar speaker makes about 60-70% of "that nice guitar tone" you hear everyday around. The speaker is essential for *right* guitar sound. You can put a woofer, but you can end up getting too much mud when you play in a band or when you try to record.
So sell that jensen and buy a new 12 inch guitar speaker if you want it really nice.
Before selling it, you can try to close the back of the cab if it is opened - it can change the feel on the lows too, so play around.

Cheers. Ace.
I`d go for some low-power AlNiCo Jensens like P12R. I`ve put mine into a DIY Deluxe Reverb and was happy.