How can I use the classical form of だろう

Question

Today I read a post here on this website (here is the post: Meaning of ～と言えよう) and in this post someone mentioned the following:

よい → よかろう = よいだろう
神だ → 神であろう = 神だろう
言える → 言えよう = 言えるだろう

Apparently this is how one uses だろう in classical Japanese. I've tried finding websites on this topic but no luck. Can someone explain how the conjugation for this works?

For example how would I turn the following words into this classical だろう form?

class 1 verbs: 書くだろう = ????
class 2 verbs: 食べるだろう = ????
exception verb: するだろう = ????
exception verb: 来るだろう = ????
i-adjective: 安いだろう = 安かろう
an-adjective: 綺麗だろう = 綺麗であろう
noun: 車だろう = 車であろう

Answer 1

They're NOT classical forms. We often use them.

And the transforming is not good. It's not wrong, but, as you can't find anything about them on the internet, there's no law in these instances. You should learn about conjugation of verb, adjective and NA-adjective, and you can take sentences to pieces of words.
Appendix:Japanese verbs
助動詞 (国文法)

よかろう　　→　よかろ　う
神であろう　→　神　で　あろ　う
言えよう　　→　言え　よう

"う" and "よう" always are after "the imperfect form" of declinable words and add a meaning of guess or intention to the words, and "だろう" is a shorten version of "であろう," so all of "だろう" can be transformed into "であろう."　

"で" is used after noun or "attributive form" and there's no distinct difference between using "the imperfect form + う/よう" and using "noun/attributive form + で" when you use it as intension, but just nuance.

Edit:
"Noun/attributive form + で" cannot be guess.
"VERB + う/よう" can be intention but adjective and NA-adjective CAN'T.

Conclusion:

よかろう　　　≈　よいだろう　　　=　よいであろう(sounds a bit odd)
神であろう　　=　神だろう
言えよう　　　≈　言えるだろう　　=　言えるであろう
書くだろう　　=　書くであろう　　≈　書こう
食べるだろう　=　食べるであろう　≈　食べよう
するだろう　　=　するであろう　　≈　しよう
来るだろう　　=　来るであろう　　≈　来よう (Verb, but only for guess. Look up "行く" and "来る." Their ranges of meaning are different from English ones.)
安いだろう　　=　安いであろう　　≈　安かろう
綺麗だろう　　=　綺麗であろう　　≈　綺麗だろう (As there're many theories of NA-adjective, you can say either the left one and the right one is the same or not.)
車だろう　　　=　車であろう