is your hay wagon a semi trailer or a full trailer. full trailer meaning the tongue is attached to a steerable axle so the only tongue weight is the tongue itself. Semi trailer means no front axle so it has tongue weight (what we think of when we hear trailer)
but no your 7.5 would not stand up to it. the 7.5 won't stand up to the V8. 8.8 would be iffy with that much rolling weight, 9" would be better but then you have the problem of not enough brakes and I don't recommend doing it but if you must then I wouldn't go any faster than 15 0r 20 mph and stay in a low gear. if it is a semi trailer then absolutely no way