Used any oil cap you want [modified-oem] make sure use OEM locking clip and 2xnuts if possible if not sit cap upside down tap bolt after nut install. Luck
I know and i agree [I DONT BUY ANYTHING I DONT NEED] try to get and USED good condition crankshaft and set of piston. DO NOT TRY TO MATCH ANYTHING, clean block and start assembly. Make sure clean area where assembly at.
Few seconds after driving= Valve seal. White smoke sort of hot sweet smell=Head gasket. Constantly smoking= Piston rings. Assuming it’s Turbocharged- Repair kit would be nice, Good luck.