This is Headers Remix for the LS3 Chevy Engine (https://www.thingiverse.com/thing:1911808).
The features are :
. Replacing factice screws by holes for real screws
. Gaskets
. Exhaust collector for driver and passenger sides

My finished project : https://www.thingiverse.com/make:743429

Printed parts list (8)
1 x Header_-_DriverSide-Remix : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%
1 x Header-_DriverSide-Collector : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x Header-_DriverSide-Gasket1 : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x Header-_DriverSide-Gasket2 : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x Header-_Passenger_Side2-Remix : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%
1 x Header-_Passenger_Side2-Collector : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%
1 x Header-_Passenger_Side2-Gasket1 : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%
1 x Header-_Passenger_Side2-_Gasket2 : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%

Accessories (38)
8 x 4mmx2mm Disk Magnet
8 x m3x1.5mm SHCS (i have cut m3x3mm to make m3x1.5mm)
4 x m3x3mm SHCS
6 x m3x10mm SHCS
6 x m3 jam nut
6 x m3 lock washer

Assembly
Attention : Header_-_Passenger_Side2-Collector is longer than Header-_DriverSide-_Collector
Look at pictures.

More add-ons

https://cults3d.com/fr/collections-de-designs/dancan13f/chevi-ls3-engine-add-ons