At 4.15 bore thats 513 ci and a bunch of stress on both the lower end and the side loading on the bores. Might be better to go bigger bore. Aftermarket block but you could possibly swing a deal on 8 sleeves to 4.25 bore. Combine with 4.25 stroke it gets you about 482+ inches and alot less stress. But cost could be as high as just gettin the aftermarket block and building a 505 -535 combo. There are few factory blocks as strong or stronger than the 59 389. Most are rare. 59 block not so rare but needs a bell and starter mount adapter. I made my own a bunch cheaper and better(well maybe not as pretty) than kits available. Kits raise cost to near halfway to better modern aftermarket block. I got $25 bucks in material in my adapter but a bunch of labor and precision is critical. Mine can serve as a midplate as well. 59 blocks are shorter from thrust bearing to bell flange(flange recessed deeper) than 61 up blocks. 55-60 (61-64) use differing bell mount starters. My adapter is fitted to a rescued original 58 starter.(thanks Mark L) I could easier use a RobMc for a Toranado/Eldorado as it has same 3.25" register and bolt spread and infinite solenoid location. But I wont need much starter on low compression turbo motor.
Personally for what you want a forged 4.25" stroker kit for a 67-74 400 block should fit the bill quite nicely or cheap out with the cast crank version.(I wouldnt) No reason you couldnt put your Cat at low 12's or better and still be a great driver.(though a head upgrade would help ease that task)
Sorry I just cant get excited about 4.75 stroke especially in any stock block.
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