[Berg]

Hi, I think you need to not duplicate an LS6 but rather build the engine you already have for more power. I think an LS5 would be easier to duplicate with what you have if you are trying to clone an engine. The LS6 came with a 3963512 casting block with 4 bolt mains, Forged Nitrided steel crankshaft, 7/16 HD connecting rods 11.25:1 compression TRW forged pistons, and there were a few different casting numbers for cylinder heads but the 3964291's were the most popular if I remember correctly. I think they were Rectangular port closed chamber heads and the engine used a solid lifter camshaft combo.

Your 1973 454 is most likely a 2 bolt main 361959 block with cast crank, 3/8 rods, flat top or dished pistons, and smaller oval port heads. There is no reason you can't build up what you have into something fun that makes plenty of power on pump gas. There are many magazine articles in archives online if you did a google search on a good pump-gas 454 build. The engine will make good torque with your original heads if you did a valve job and changed out the pistons for a little more compression. There are hydraulic camshafts that are far better than anything that was made in the 6o's and early 70's. You can find something with a good amount of lift and duration, maybe even a dual pattern camshaft. You can get coated pistons and low friction rings, keep the 3/8 rods and have them machined with quality bolts and stud the main caps. A properly balanced rotating assembly will give years of reliable service.
The best place to start is pull your valve covers and see what the casting numbers are on the heads. If they are decent heads, rebuild them and run them. If they aren't so desirable you could step up to a set of aftermarket heads. The secret to big block and any internal combustion engine really is to be able to move air and fuel in and out as efficiently as possible. For a street engine larger oval port heads will provide good low end torque which most people don't realize is more important than horsepower. Sorry if this was a little long but I wanted to help you understand what you have and what you could build with what you already have without spending way too much money. I hope this helps you out