Maybe a 331

331 will need a new crank , rods and pistons. Going to a 302, may just require a crank and rods, depending on how good your bores are. Does your motor use oil ? Burn oil? run bad? How much money do you have to spend ? The 331 I have cost me about $1500 for just the short block to build.

Look at the casting numbers above the starter. One group will look like this; C60E-6015-A (not necessarily those exact numbers, excepting the "6015") That will tell you if the block is a 289 block. "C6" translates to 1966--"C" is for the 60's decade, "6" is the year the model year the block was first cast. 6015 is the engineering number for an engine block. Next to these numbers, will be a number/letter/number(s) group, this is the date code, the actual date the block (or any other part) was manufactured. First number is the year, the letter is the month, starting with "A" for January thru "M" for December, skipping the letter "I". Last number or numbers is the day of the month. If this is the original block, it will have been cast up to a month before the build date of your car.

Your 289 block will be fine for a 331. The cylinder skirts are very close to the same - to the same - as a 302 block. I have one resource that states the bores a slightly longer, but this seems to not be the case in practice, else the variation between blocks is so great that the small difference gets lost in the "mud". Anyway, stroking is okay. You can use a cast crank (like a Scat) and cheap forged rods (like Scat) and not be in it for much more than a 289 to 302. The torque difference is big with the stroker and I would recommend it for your stated needs (stop light torque, baby!). Your heads (if you already have them) are fine for under 6000RPM operation and a modest cam profile. I would upgrade to the Comp XE274HR for a roller cam. Something similar to those duration numbers if you stay flat tappet.

As for 331 pistons, Mahle (using 5.4" rod), DSS (5.315" rod), and Probe (5.4" rod) have pistons that do not have the pin encroaching the oil ring and, therefore, do not require an oil land support. An oil land support, if correctly mounted, should not be a problem, but distorting the support when installing it is (loss of good oil control). For DIYS applications by amateurs (like me), I recommend one of the above pistons just to keep down the risk of a mistake. I used the Mahle Power Pack (pistons, pins, rings, locks) and am happy with them.

Do the 331 or 347 for $4-5k you can build a nice strong reliable engine.

You may want to consider ditching the 289 block and using a late model 5.0 roller block to build a stroker.

use your 289 block and get a balanced rotating assembly from some place like DSS. that way you ge tthe complete kit of crank, rods, and pistons, as perhaps rings and bearings as well, as a matched set ready to go into your block. have the block checked over for any machine work that it will need BEFORE you order the kit. as for the cam and heads, socalcruising has the right idea.