Any issues with swapping from 396 to 454 HO in 67-72 Trucks?

[Jonlopes]

A few months ago I posted some questions and a video about the knocking sound in my 402 big block.

Preparing my-self for the worst case scenario I started calling around to the machine shops in the area. The strange thing is every single one of them were completely flabbergasted with the insane notion that I was hoping to drop off the truck and have the engine rebuilt. Apparently this simply is not done. They all want me to pull the engine from my only truck and somehow transport it to them so they can do their thing. Then the prices they are quoting also seemed high in the $3500 range. I guess this is a good sign for the economy since they are able to pick the low hanging fruit and turn away the rest. To me this seems like too much work (rent a truck twice, etc) and money for an engine that has already been rebuilt once.

In my youth (25 years ago) I pulled and replaced a couple of engines so I started looking at alternatives and I ran across the Chevrolet Performance 454 HO. It costs a little over $5k but it has all brand new parts and puts out 425 horse power which is more than I will ever need, a 2 year warranty, AND shipping to my house is included. Costs a little more than rebuilding my old engine but the parts sound like they are not only new but better quality (4-bolt mains, forged crank, etc). I will have to buy or rent a cherry picker and an engine stand but Harbor Freight always has them on sale.

I am hoping someone has the experience to answer a couple of questions:

Does anyone have experience with this swap (stock 396/ 402 for new 454 HO)? I am hoping it will be a simple unbolt everything from the old engine and bolt it to the new one. Are all of the bolt holes drilled/ tapped in the same place?

My truck has the short water pump, I can buy a correct one and swap out the long one with no problems but after I change the pump can I just bolt up all of my pulleys and accessories and have them line up correctly? Is the distance from the engine to the pulley mounting surface of the Harmonic Balancer universal or are there different sizes? Or in other words is the harmonic balancer different in long water pump applications than short? I am assuming no but it would not be fun to get to that point only to find that my pulleys do not line up.

The stock oil pan is like 4-5 quarts where the 454 HO has a 6 quart “truck” pan. I would rather have the extra capacity, will the 6 quart pan fit?

I know this question has been debated for decades with no firm answer but am I silly to want to keep the stock exhaust manifolds with an engine that makes 425hp? I have had several cars with headers and hated them every time with the starter heat soak, leaky flanges + gaskets, not being able to get to all of the spark plugs, etc.