3.58 stroke x 340 main (rods/pistons?)

A few tidbits that may or may not be worth considering:

When mixing parts, watch the crank counterweight clearance to the underside of the pistons.

If it's within the budget, Eagle SIR rods are forged from 5140 steel. Scat I-beams are stronger being forged from 4340 steel, but more expensive. However, the Summit brand I-beam may be relabeled Scat I-beam and only slightly more expensive.

Stock type pistons are on the heavy side and I personally wouldn't feel comfortable using SIR rods with them.

The lightest piston & rod you can afford would provide extra durability & performance benefits. Not sure if it would be more affordable to balance externally and probably remove weight from the crank or balance internally and add probably add Mallory metal. It depends how the crank counterweights are made/weighted. Internal balancing would be helpful especially when using a flywheel.

I ran a Scat 360 cast crank, SIR rods and light SRP piston combo. (Not sure if there is a lighter "shelf" piston available.) Crank was neutral balanced or may have needed very little Mallory Metal. Scat I-beam rods are slightly heavier than SIR.

Using more common & less expensive 915, 587, 596 heads and enlarging original 1.88" seats to accept 2.02" intake valves with "fresh, high" seats will likely provide a performance gain over trying to optimize original 2.02 seats in X-heads that may have had multiple valve jobs over the decades and may be "sunk".

I ran a bracket combo many years ago using a stock 360 crank, bushed OEM 340/360 rods and Direct Connection pistons for a 3.454" stroke crank. (Used for 355 Nascar engines.) Piston tops had to be milled to get around "0" deck without the need for extra decking of the block, which reduces the need to mill the heads and/or intake to get the intake bolts to line up. The underside of the pistons also had to be milled underneath the wrist pin bosses & skirts for counterweight clearance. I don't know the final weights & measurements but it made the pistons a good bit lighter. (I recently saw some of those pistons for sale somewhere.) At "0" deck, compression may end up too high for the street and I don't know what the piston top thickness limits are.

The Direct Connection 3.454" crank pistons & SRP pistons have generous valve pockets.