There should be a number stamped into the block next to the"GM" Its most likely on the left rear of the block as your standing behind it where the bellhousing is attached. If you look up that number, it will tell you small block, big block, what size ect. Do a search on google for engine casting numbers and you will find lots of sites where you can match up your numbers. As far as getting that many hores out of a, lets assume small block, Your probably talking around 3500.00 to 5,000.00 depending on how fancy you get with the heads. Just a idea, but you might want to check out a "crate" engine from summit racing or somewhere like that, you can buy them already assembled, almost turn key for around the same as building it yourself only without the banged up fingers and long nights in the garage not to mention they come with a warrenty! Here is an example of what the number might look like GM 3970010
That's the number on mine and it's a 4 bolt main 350 made from 77'-79'
Any other question, i'd be happy to help. Good Luck!