1970 engine options

[ofnaman]

Hello all,
I am new to the site, and have just brought home my new project: 1970 c 20 2wd longbed. I have been trying to figure out what the original engine in my truck was and if it is still in it. I cannot find any info on engine options anywhere for 67-72 pickups, (although I have not looked very hard in all honesty). The glove box states it should have had a 400 cid v-8 in it, rpo code L47. The truck has a big block in it now. I am not sure yet what engine is in it, I have not had a chance to run the block #'s. It also has the original 400 turbo trans in it. Does anyone know what the L47 400 cid engine is? I have seen some of these trucks with a 402 in them and was wandering if that is what the L47 is. Thanks alot.