Assuming the motor runs well top end is still good the Biggest bang for the buckSSS will be a modern big pipe Q pipes, HPR, AAen, Mitches pipes)-- but before a big pipe rechamber the head so you dont destroy your toy and it will run better too. If the 87 carb is stock it needs some mods and be dialed in..  Stock the 87 carbs like to lean out on deceleration and cause problems.

Order of importance in my opinion
1--carb dialed in
2   -head properly done--oring is nice to have and saves money in long run but not necessary if $$ are very tight
3- pipe

Of the 3 yourmost  power is in the pipe, but you need to address the first two of your joy would be short lived.  MY m.02