Good news on the bottom end and bearings. Time to check the cam. You could probably remove the timing belt and see if the engine spins more uniformly (spark plugs removed) to help determine if the binding is the cam/accessory drive or the bottom end. There could be a rusty piston wall now that I think about it.
Both the engines I bought were "running good" but both had really trashed cams. If the bottom end looks good, it could be a cam swap away from a running good.
"Burned rubber and ran strong" Also had spark plugs that stuck a 1/2" into the chamber that were black as coal.
"Ran great when pulled a few years ago"
The follower rubbed the keepers and retainer on the left valve.
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"How I learned to stop worrying and love the OHC Pontiac L6"
The Silver Buick- '77 Skylark coupe w/455, SPX, MegaSquirt 3 & TKO-600 (Drag Week 2011, 2012 & 2015!)
1969 Firebird with a turbo'd Pontiac L6 controlled by a MegaSquirt 3 and backed with a microsquirt controlled 4L60e and 4.56 gears! (Drag Week 2018!)