just trying to give it a little more HP>
Find a copy of "The Buick Free Spirit Power Manual" and read it.
Change to the odd fire 231 HEI distributor,
change to the late 231 heads; Verify that the cooling ports to the block line up first.
do a quick port grind to clean up the area immediately around the valves,
Install tulip valves and a 5 angle valve job.
Install decent valve springs (at least 90 to 110 lbs when closed),
Change the cam to one with decent specs for towing,
Install a Cloys tru-roller timing chain at 4 to 8 degrees of advance,
change the rods to the late 231 rods, (shot peen and magnaflux the rods before installation)
Install a good grade of hypereutectic pistons, avoid chrome/molly rings they can be a bear to seat properly,
find a GOOD Rochester 2GC 500 cfm 2bbl carb off of an old 350 Chevy pickup and rework it (worn out parts will have issues). Note; this may require grinding on the intake manifold to allow for better flow immediately below the carb.
Install fully grooved main bearings and a high volume oil pump.
Rework the oil passages in the timing cover to get better flow,
Install the longest primary length tube headers (30" or longer) that you can find (you want a relatively small primary tube, 1.5" or smaller) shorty headers will increase flow but do noting for torque except at very high rpm.
It would be cheaper and easier to change out the engine...
If you hop it up and hot rod it with the current rods and pistons; expect it to come apart...
HEI odd fire distributer,
late (80 or newer) 231 exhaust manifolds, this will probably necessitate a new exhaust system...
Rochester 2GC 500 cfm carb.