A 6-71 on a 540 is kind of small, need to spin the blower faster to get the boost you want...
I would suggest keep the heads and invest in a larger blower, a 10-71 or 12-71. or even a 14-71. THere is not a big price difference once you get over 8-71. Going to an 8-71 would not justify the cost.
There are always good used blowers out there, or something rebuildable at a decent cost...
I see you are on a budget, the suggestions are only if you have or want to spend the money. You can still use the 6, and change it later. Blowers are easier to change than heads.....