Would this be a workable combo 4.375 bore 2.06 comp height 4.25 stroke and a 6.535 bbc rod.

You’ll have 0.005” pistons above deck by my math, assuming 10.725” deck height. Not sure if you'd have trouble between the pistons and counterweights

Most 4.25 cranks have a minimum rod length listed in the catalog. Double check to see what the mfg says. I'd use a 7.10 rod in an RB block but I have used 6.535 chevy rods in low deck engines. Also, if you haven't verified the deck height of the block then don't assume that it meets factory specs or that it will clean up at factory specs. Most Mopar blocks need to be cut a bunch to square them up.

The crank counterweights will have to be cam cut a LOT to clear at BDC. Add mallory metal to balance it and its not worth it.

Here is a rotating assembly that I used in my Duster engine. This was a low deck with a 4.250 stroke Callies crankshaft, 6.535 Crower rods and then a set of semi-custom pistons from Diamond. We had to turn the counterweights down on a lathe but I don't think the crank required any metal to balance. I think we just had to dimple it and it was good to go. The rotating assembly was fairly lightweight. Around 2300 gram bobweight I think. This was a fairly expensive engine to build. These days with an RB block I'd use a stroker kit with 6.800 or 7.100 rods and call it a day.

Do you already have the pistons?

I’m guessing you already know, the 2.06 piston is for 3.75 stroke with a 6.76 rod

Yes I know I was just curious if it was possible or not it would probably interfere with the crank. I had found a set of piston new with the 2.06 comp height.

that's an interesting idea, I have 6.535 and a 4.30" stroke in my low deck 517, I Suppose if the piston skirts were dimensionally the same as a low deck 451 or 511 (1.32" CH slug) the compression height above the pin might not matter as far as rotational clearance, Heres a pic of my JE pistons and short block. I think my Compression height was like 1.30"

But if you are talking about like an OEM type six pack or TRW 11.5 domed slug.....I would say no way the skirts are way too long.

If you have the crank and rods already build a low deck or swap out the rods. if you have the pistons maybe sell them to someone with a low compression 440?

But if you're building it from scratch and you have to get pistons made anyway....It would probably work if the skirts are as I stated before.

The longer the rod the less side-loading it does to the cylinder wall...I wouldn't do an RB with anything less than 7.1 rods IMO.

I would pass. Do it with the right parts and you will sleep better. I am always in favor of the most cubes you can work into a combo at a reasonable cost, especially for a dual purpose combo. A bigger motor makes more torque down low, and takes less time to get through the first half of each gear, having more average HP down there. Add in the benefits of less required rpm on valvetrain, more stall from the same converter, the list favoring a big stroker is long. Just keep within the reasonable strength limits of the block you run.

Long rods would be better in terms of longevity....at least in theory

That said the Pits are full of 9.8 deck 496" BB Chevies with 4.25" cranks and 6.135 or at best 6.385" (+.250) rods.

I have 6.2" rods in my 4.25" stroke 440" Mopar smallblock and 6.123" (340 mopar rods) in my 9.5" deck 427" Windsor ford.

I just ordered an Ohio crankshaft rotating assembly for a 505 build (4.350 bore opposed to 4.3750) for an RB. They worked with me on the piston I wanted and the 7.100 rod opposed to their advertised shorter rod. It was very reasonably priced in my opinion. Comes with bearings, rings, and it’s balanced.

Yes, less side wall loading but what I really like about the longer rod is that it keeps the pistons out of the crankcase. The further you can keep the pistons away from the big rotating cloud of windage the better. Some engines such as SBF and BB Chevy engines make do with short rods. The short rod motors run hard, but given the opportunity I prefer to use a long rod.

Something to consider about the tall 2.06" pistons is these will have inherently more stability than a much shorter C.H. piston which could maybe offset some of the side load issues being discussed. IE. It should take longer to become a skirt/ring wear issue if at all. J.Rob

I ordered the same kit from Ohio Crankshaft with the 7.100 rod and 4.360 flat top piston about 8 years ago now. It worked out great.
Regarding the 2.06 compression height I wouldn’t want to carry the extra piston weight .

The other question you need to consider is how much HP are you expecting to make with this combo? Over 650HP stock Chrysler 440 blocks are not very durable in my experience.
I just did a 400 low deck with a 4.25 crank 6.535 rods and 4.380 bore got the kit from 440 source. Very little grinding and fitting worked slick. This was a mild 512 engine for a 4x4 truck. Small hydraulic roller 10 to 1 compression 452 heads hand ported Fi/Tech injection it made 500HP and 520 ft. lbs on pump gas and idled at 17 inches of vacuum.