I think you will be ok.
Last week I threw my grandpa's 5x12 trailer on the bumper of my 87 and loaded it up with what sounds like a heavier load.
Like the others said, try to keep the heavier stuff towards the back, and even put some stuff in the bed if you can.
Just be careful, stay out of OD, and if you have an auto make sure you hit that OD cancel button.
I think you're forgetting some important things...
The step bumper on your 87 is considerably stronger than the ones they put on the 98+ Rangers. These new Rangers, the bumpers look like they've been made entirely of really heavy gauge sheet metal bolted to the frame compared to the beefy metal that they used to use. I trust the bumpers on my BIIs a lot more than the bumper on my 00 Ranger and my F-150. And that is why both my Ranger and F-150 sport Class III and Class IV hitches (respectively).
Heavy stuff on a trailer should always be balanced over the axle unless that is either physically impossible (boats are notorious for this) or if it gives you too little tongue weight.
Experienced trailer haulers will often situate a load on a trailer to suit the particular needs. I heard of a trailride where everyone had parked their truck and trailer in a field... which got muddy during the day because of rain. Most inexperienced guys tried to load as far forward as possible on a trailer thinking that the increased tongue weight would give them traction, but instead the sank and had to use their trailrig to pull their tow rig out. But one guy who had hauled a lot of trailers (and grew up on a farm), loaded his trail rig up as far back on the trailer as possible and was able to drive right out (where he put the trail rig back where it needed to be on the trailer).
There is a lot of tricks to pulling a trailer.
And yes, stay out of OD. If it's an auto trans you'll want to put an aftermarket trans cooler on if you can afford it. If it's a manual, use your gears - don't be afraid to wind out a gear. Your rev limiter will kick in before you hit the redline (or it should) if you don't have a tach. If you do have a tach, you'll want to shift between 4,500 and 5,000 rpm.