advice on speakers?

[Foxcroft80]

Hi All,

I have a '68 c10 with currently a clean dash (face plate where radio once was). I like this look a lot as it keeps the inside simple. There is an iPhone hook up in the glove box which goes out to a Kicker brain mounted under the dash. Currently my only 2 speakers are a 6" on either side of the kick panels. These were all in one speaker kick panel set.

Anyway, I need to get some more speakers in my truck to round out the sound. I'm not looking to spend a million buck but do appreciate a decent system in my vehicles. My gas tank is still mounted behind the bench seat so the only real estate free is under the seat, which doesn't have a ton of clearance. Any ideas on speakers to look at, or do I need to get custom boxes made?

Thanks,
Foxcroft-