Are there roller lifters and cam that I can drop in my 340 with no modifications

There are no drop in hydraulic roller setups for 340 LA, if for no other reason than there is no standard pushrod length for any of the aftermarket lifter options. A mechanical roller doesn't have the height issue with a simple slug and roller tip.

Hughes makes (sells) hydraulic roller lifters that have the link bar out of the way against the block and oil galley gap in correct location, but to work the design has a very tall lifter cup that needs a very short and highly angled pushrod. The pushrod length needs to be determined with a measuring pushrod with the correct ends that can be adjusted until the valve tip contact is optimal through the cam lift cycle, then sent off to a shop like Smith Brothers for a custom pushrod fabrication. There is no way around this procedure. Part of building an LA roller motor. Avoid any claims to the contrary, and avoid eBay lifters.