Is it a chrome dipstick tube? I find the end is too long that goes in the block is too long. I grind it down but the flared that seats in the block sits loosely in the block. I believe that it does fit between the manifold and block. If you want a tight fitting dipstick, the ones Supercars Unlimited sell fit very tight. Throw a gauge on it, the 455's quite often get over revved and that causes bottom end damage, which could be the low oil pressure issue. Tell us what it has for oil pressure, something like 10W40 or 20W50 might limp it along, depending how bad it is.
It is a chrome dipstick. I think it's a Mr gasket brand.
The guy said it had 30 psi? Lbs? I'm having a brainfart on the oil reading unit of measure lol. He said he was driving and saw the pressure dropping down to around 30. He then filled the oil up to where it was supposed to be and then continued driving with the same result.
He had mentioned the first time I went out there to look at the stuff something about the dipstick and him having to do something with it. Dipstick isn't there and I did find like shop towels in the area where the dipstick might go. I say might because I can't actually see where it goes.
That's all the story I have on it. I'll get more facts as I dig into it and keep you guys posted.