I have a gen 4 block which I'd like to refurbish.
The bores have a mark just where the rings stop. I measure 0.003 inch or 0.07mm bigger than the original bore 4.25 inch.
In general the cylinder walls are about 0.03mm off.
Is it possible to hone the 0.07mm or do I need to go for oversize pistons?

I heard about piston with a self adjusting coating on the skirt. Would that be an option?

If you have to buy new pistons buy a whole new rotating assembly with a stroker crank. You’ll save some coin on the pistons that way

What pistons were you going to be using? If you’re replacing, it’s easier to find what you’re going to want in an oversized piston vs standard (better options).

If it were me, I wouldn’t cut corners here. Just bore the block and as mentioned above, bump the displacement with a 4.25 rotating assembly. You’ll get better rods out of the deal, too (reconditioning rods with good bolts is almost as expensive as a set of H-beams).

If you are wanting to keep the budget low, line2line makes a nice coating that will let you use your pistons over.

Well, I am still not sure what to do. Since I am located in germany, I think line2line isn't an option unless they sell new std pistons with a coating. I also wanted to go for a -10cc piston. But I guess that will be not cheap as well.
Boring and honing is around 950$ around here so I am considering just honing and putting std pistons in.

The rotating assambly is not in my budget for that engine. But I am aware of that option, and want to go that way for a gen 6 with missing crank which I have waiting here.

The problem is, coating the pistons will not correct the .003" wear at the top of the ring travel. Realistically to make the bores straight and round again they will end up being .010" oversize. At that point you might as well just bore it oversize and go with new pistons. As far as doing the stroker deal that all depends on what you are trying to accomplish.

what I expect from the engine:
cheep replacement for a 454 330hp with a slightly higher compression and a bit of valve-job, retro roller lifter and rockers.
If it would be somewhat over 330hp later I'd be happy cruising my 245 Cris Craft at mostly 3000 to 3500 rpm.
Euro gasoline 95 octane / equivalent 90 octane US

The facts:
454 probably 1977 no serial around
Bore 4,25" +0.0012" roundness // +0.0028" at the end of the ring travel
Pistons: I can not notice wear on the original pistons. Clearance (to original bore 4,25) 0.004"

So far with my math after honing I would end up at a piston to cylinder clearance after honing of ~0.007"

I am no expert at all
but isnt 0.007 a little too loose? I thought everything needed to br between 0.00275
and max 0.00325 !

Hone what you have and put file fit rings on your old pistons. Millions of engines get rebuilt this way and run great. An extra .003" on a piston bore is nothing to worry about. If you want to gain a little compression you can go to a MLS gasket from Cometic that is only .027" thick VS the original that is .041 thick. Also, the heads can be decked for more compression since you're using a flat or dished piston.