Kip,
I have had a number of Trac Vac and competitive vacuum systems over the past 20 years all used with 60 and 72 inch decks. Vacuum systems take a LOT of power to work well. By that I mean in order to keep up a good fast air flow even when there is a lot a debris in the stream, you need a big power source. All of the tractors I have used vacuum systems with had at least 20 hp and the vacuum itself had 8 hp or more. Thus with a theoretical total of 28 hp to apply you would think that is plenty of power, but even this is insufficient under a lot of conditions.
Currently I have a 31 hp tractor with a 72 inch deck. Last year I upgraded my Trac Vac blower to a large unit they normally sell for loading pickup trucks. This was done at the recommendation of Eric Smith of the Customer Support Group at Trac Vac. Normally they power this truck loader with an 11 hp engine, but since my system has very long hoses I went on up to a 13 hp engine. It works exceptionally well. So far it has never plugged. My greatest problem has been to keep the hose clamps tight enough to keep the hoses connected to the metal parts. I resolved that by installing the heavy duty clamps that spiral around and then overlap the hose wire.
If you have a very large tractor, a PTO powered vacuum may be practical. Otherwise I would stick to a separate engine on the blower. Maintaining that seperate engine is not that difficult anymore assuming you take care not to let fuel get stale in the tank.
JackIL