Hello and Welcome
IERICKYP!
This forum tends to be more focused on original GMC V6 trucks however...
I did some quick research on the sister 67-72 truck Forum and found this link.
https://67-72chevytrucks.com/vboard/...d.php?t=369663
It has basic swap information, not on an LS, but an early 350. The truck is also a 1960 and had those welded in frame rail mounts. Looks like he did a crossmember swap and cut those mounts out. I've never done an LS swap.
I've included a link as well to that forums LS parts section.
https://www.67-72chevytrucks.com/vbo...play.php?f=247
Anymore photos of your truck and does it still have the early hood?