A 2 bolt main motor and 4 bolt main motor? and could you also list pro's and cons?

 

2 bolt main = 2 bolts in main cap
4 bolt main = 4 bolts in main cap

4 bolt mains are rumored to be stronger.

 

a sbc has 5 mains on a 2 bolt main block all the mains have 2 bolts. on a 4 bolt main block the 3 middle mains have 4 bolts and the outer 2 have 2 bolts. a 4 bolt main block keeps the mains from moving around. if your not making over 500 horse or turning over 7000 rpm it really doesn't matter. a 2 bolt main will work just fine.

 

if you ever wanted you couldn't use splayed caps on a factory 4 bolt block

 

It's just insurance to have a strong motor, like forged pistons or crank.
but like rokn91rs mentioned, it's not usually that important, in spite of the fact that most hot rodders will only use it because of it's rumoured higher strength. unless you rev it really high, or make tons of power, then it's not that important.
and remember, you can machine a 2 bolt main for 4 bolt splayed end caps, which are even stronger. you can't do that with a 4 bolt main.... kinda a catch 22 I guess....