Need help on oil level dilemma in my new to me 454

I recently purchased a big block 468 that I have zero build info on except for the cam sheet. Yesterday I drained the oil for the first time, and it had a LOT of oil in it. When I filled it back up, I'm at 9 quarts and still a half quart low per the stick! I don't know the year of the engine, it's so shoehorned in this second gen Camaro that I can't see the numbers on the block. It was built by a local well known race engine builder and was intended to be installed in a pro street car.

The pan looks stock as in it has no bump outs and all edges are rounded like a stock pan, the drain is on the bottom. I have no oil cooler and I have a large WIX oil filter installed. The pan hangs down about an inch below the cross member.

I put a straight wire in the dipstick tube, it is 24 1/2" deep, the dipstick is 20 1/2" long, the full line on the stick is at 19". All of that being said, the pan would have 5" of oil in it when the stick would say full.

Does any of this mean anything to you experts that would tell me 1. Do I have too much oil in this thing and it's at risk of hurting something 2. Do I have the wrong dipstick and the oil levels read wrong, 3. Do I have an 8qt stock looking pan and with the addition of a big oil filter everything is normal?

If I measure the deepest part of the pan as compared to the shallow part near the crank and that difference is greater than 5"m does that mean that I'm safe?

No, mine has more rounded edges like a stock pan, it's even painted black like a stock pan.

I filled the filter my hand before installation. It took most of a quart and probably would have taken more if I kept waiting for the media to soak up more oil.

Some oil pan pics as requested
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Sorry that my pictures got all wonky. BTW, all that brown stuff is from where the car was stored. It was an old steel mill, now storage facility, and its full of that brown dusty crap that I need to clean off.

I contacted the builder, he was no help at all. I gave him the name of the customer but I don't know the build date. He said that all that he could do was pay his accountant to go back through a few years of receipts to try and find the original receipt, he didn't sound interested in doing so. I'd be willing to pay what it cost if it was reasonable. Since then I met a guy who does a lot of business with that shop. He is going to try and use his leverage to get them to look through and try and find it.

What you really need to know is......Where is the oil pump pickup located in relation to the bottom of the pan? If it's within the normal 3/8" to 1/2", then you would dump in 5 quarts of oil and make a new full mark on your dipstick. This will require records from the builder or pulling the pan.
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Use a fiber optic to get a peek at the pickup through the drain hole.

You can get them cheap that work with a cell phone.

I know it's probably redundant but I have to ask, is the motor running when you're checking the oil level? Motor needs be off (not running) when you're checking the oil level, if the motor is running you may be able to get 9 qts in a 5 qt system.
Sorry, don't mean to insult.

No offense taken, it’s a legitimate question.

Motor is off, sitting level, has been started so the filter is full, I put oil in both valve covers, and the returns are not clogged.