I’d start by confirming true top dead center with a piston stop (in case the mark on the balancer is wrong), and then set timing. I’d also double and triple check plug wire routing. In my experience these engines run surprisingly well with 2 plug wires crossed.
If you have an auto trans, especially the ‘65-‘66 green dot version, any chance you are starting in second?
"When a woman is a really good driver, she is just about perfect."
- Raymond Chandler
'66 GT Fastback show car, nightmist blue, warmed up original 289 & T-5Z, 3.80 trac-loc, AC, PS, pony interior, Retrosound, rally pac
'66 Coupe driver, Bullitt green, 302HO w/ 351W heads, roller rockers, Holley 600, T-5Z, 3.55 trac-loc, collapsible column, tank armor, disk brakes, shoulder belts
'11 BMW 335i X-drive, 6 speed manual, all the bells and whistles