I am thinking about getting a Peavey Valveking 112 and I was going to change out the speaker and drop in a Celestion Vintage 30. I was wanting to know if anyone has done it because I have heard that the Vintage 30 won't fit into the 112 because it is to big. Is this true?
I own a peavey classic 50 and also popped some celestion30 speakers in it sounds Amazing, for your amp, i'm pretty sure that all peavey amps have a custum size you can fit so yeah i think you can
Vintage30's sound best when used inside 4x12 cabs. Though should be a big improvment over the stock Peavey speaker. The Celestion G12T-75 is ideal for combos if youre looking at Celestions.
I installed a V30 in my El Diablo combo and it sounds badass.

Although I can't say for sure about the VK, a 12" speaker is a 12" speaker, and I don't see why you wouldn't be able to fit a V30 inside a VK combo. I've known people who've switched their stock Peavey speakers with various Celestions (with a XXX, Bandit, and 5150), and they've always fit without a problem.
Guitars: Custom Lado Earth 2000-3, Custom ESP Explorer, BC Rich KKV, Gibson LP Studio, Greco SG, El Degas Stratocaster, Agile AL-3000, LTD EX-351

Rig:Marshall JVM410H + Marshall 1960A, Boss Noise Suppressor