That looks like the stock truck oil pan which is one of the lowest hanging versions. Does it look like a front sump pan would clear if the crossmember was welded back into place? You could try a GTO pan for that. If rear sump is all you can fit then there are plenty of stock (fbody) and aftermarket versions available. I think Holley makes a few "muscle car" pans.
Definitely check if a starter will still bolt to the block. You may need to use a different header.
Looks like a solid base. I think that's an nv3500 trans. Which isn't bad but it would be much easier to use a t56. More expensive initially but you won't spending money along the way to 'solve' problems the nv3500 brings to the table that the t56 doesn't. Also, a 97 or older t56 won't directly work on an LS engine without a decent amount of modification.
