PTO generator inverter

Yeah you could go a rectifier and use the diodes from a old style welder and the heavy heat sink and then back through an inverter,, thats a real nice way to go and would remove just about any noise from the generator head,, but that would be a big unit,,, might be better off it you can find a few big capacitors ( think surplus computers supply for an industrial set up) that would take the noise out and give you a little bump when things kick on. You said 308 vac I think you mean 208vac, if you were to go that rout Xformer it down to 48 vac then use the rec. and then back through an inverter and xformer to 208
But unless you are running a bunch of very sensitive equipment. You really dont have much to worry about ,a filter cap would take care of it if you are worried, and if you have the tractor set I would think, unless you have a 2 speed PTO, you are running just about WOT anyways. Most dips are say 2 to 5 cycles which might give a peak amp for 1 cycle on a motor start up and the can go to 1300% of run current but in the short cycle time involved its not a big deal. NOW if you were say starting something that was running at almost the full out put of the head, then you might have some issues

You could add a 'flywheel' on the PTO-genny shaft. The heavy spinning mass will 'smooth out' the genny output.
big portable welders have a simple setup to go from idle to 'run' by monitoring the current of the arc and controlling the throttle. For power control,I'd use a PIC controlling a servo, 'tuning it' would be the fun part.
another way is to use 'solar power' controllers. They typically convert high voltage DC into AC.
considering the huge number of PTO gennys out there without 'feedback' I think you're worried about nothing.
what is important it that you use properly sized cables to feed the power from genny to the loads ! Do NOT use itty,bitty 18ga extension cords ! Big, fat ( 10ga, 12ga) cords are a must. There's online 'calculators' that will tell you what's needed.

FWIW Amazon has a selection of AVR's ranging from $30 to over $200, depending on what you need. My PTO genset came with AVR installed from the factory. Paid a little extra, but to me worth the price. With my older genset I couldn't use a computer or use SAT TV as the screen would be nothing but lines. Now I can't tell the difference between commercial power or new genset.