I'm currently rebuilding an 350 chevy v8 and bought a new crankshaft and wondering what type of harmonic balancer do I need since the snout of the crankshaft has an engraved type of grove.

Here's an picture of the snout.


https://i.imgur.com/GQ6gkxe.jpg

 

Same as any other SBC crank...

But first, you need to put acoupla Woodruff keys in the grooves.

https://www.google.com/#q=woodruff+key

 

There are as many balancer options for the SBC as there are paint colors. The main thing is internal vs. external balance. The 350 (3.48 stroke) was always internally balanced and takes a "zero balance" damper(harmonic balancer). The 400(3.75 stroke) was externally balanced and, with the exception of high performance aftermarket cranks that are balanced using heavy metal, require a counter-weighted damper. To save confusion, the one piece real main seal SBCs, while generally still considered internal balanced do in fact require a counter weighted flex plate/flywheel due to the lack of the two piece rear main seal's rear counter weight.

Aside from this int vs. ext balance consideration, you can use any type of balancer your heart desires. If you plan on running high revs very often(I notice that your new crank is lightened and fileted), you will probably want either a damper with lock rings(SFI approved) or a one piece like the fluid damper.

 

Yes your "groove" in the crank snout needs woodruff keys added to it. They should come with the cranks but they dont.

For a good cheap damper I like the professional products power force ones.