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5 liter roller block Is the place to start unless you are planning on making over 500HP, then I'd use a new aftermarket block like World products or Dart.
My current 331 is based on a Dart block. Just my opinion that it is money well spent.
 

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it is all a matter of how long you want it to last and how much power that you will ultimately make.

a late model roller block is the WEAKEST block to use...
thinnest bores, thinnest main saddles, shortest lifter bores (must use corresponding late model hydraulic roller lifters with the flimsey tin metal spyder hold down)

the mid year 79 to about 85 block is about in mid strength and you can use a LEGITIMATE length linked lifter ( stronger and no spyder) along with the thicker main saddles and cylinders..

then actually the blocks from about 1971/73 to up to the 1979 groupings are the next .."second strongest"

and then the 1968 to 1971 blocks are the strongest stock blocks pother than the same era legit original BOSS 302....NOT the same as any other boss 302 offering in later years (FAKE BLOCK)
....the original "289" is right there in strength too...only concern is proper previous machining and such....
... with a concerned eye on water jacket rust internally...
there is a small concern with the rod and piston lengths at one time..but really is not much concern or thought of/about since the 325 / 331 cu.inch engines strokes are not an issue with the larger volume pistons makers such as PROBE...it is all about exact piston shape of the skirts and positioning of ring lands...
this is because the 289 cylinder is only from .080" to .0100" shorter on the underside...no problem..
and you can use the legit longer length linked lifters if you wish to use a hydraulic roller design.. if it is a solid roller lifter..then..no problem..that is what they were made for...
 

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If you can find a set of main caps from a Mexican 302(or a hi-po 289, they're the same) for whatever block you go with, that would help to some degree. Some would say the Mexican 302 block is the superior 2 bolt production block but I'm not sure the "higher nickle content" myth has ever been proven.
 

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agreed.. the mexican blocks are getting pretty hard to find..but they are as good as the same erayear- early blocks...thicker main caps.. but if you find the caps and the block, then unless the mexican block itself is un usable..why put the caps on another 289 or 302 block...why not just run the mexican block...???
 

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You can find the caps on eBay, sometimes even CL. I use to get my dad to bring me the Mex 302's when he would drive back and forth but too dangerous to do that now.
 
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