will a 2001 lb7 fit and match up in a 2003 lb7 spot?

Mechanically, yes.

Intake y bridge is different, just use the 01 intercooler boot to make up the difference there.

Oil pressure sending unit is different, hence the wiring harness is different.

Belt routing is different, thats more of an accessory thing, so may not matter.

Use the 01 engine, just swap the wiring, OP switch and accessories, would be a decent idea to swap the intake if you want it to be a direct fit.

hey do you guys no if i counld put any lb7 in my 03 gmc as far as emmisions shit my truck got california emssion but live in ct hard to find a motor but there is plently of nf2 and nf4 emmision motors