willysmjeeps.com

Picked up a 350 lb. weight for a willys snowplow, any info out there how these were attached to the frame?

That depends on which of the many types of balance weights you have. Post a photo so folks can see what you have. Wouldn't do much good to explain a hitch connected weight when you have a frame mounted weight.

For my plow jeep I always used four bags of sand (75 lbs ea) tossed in the rear bed.

Are you sure that's for a CJ or M38A1? The only Willy's vehicle I have heard of using a weight is the 81" FC150 Forward Control.

It was mounted in the rear frame to stabilize the vehicle.

It was used a lot of years ago on a CJ5..It mounts to the frame, It even has reliefs where the springs would hit. Your three bags of sand sounds better than putting this on every year.

a heavy front bumper weight had been an option/accessory on early jeeps since the cj2a. The weight was placed on the front of the jeep on the front frame rails. This helped balance and improved traction for the vehicle when plowing fields, etc. If my memory hasn't failed me it weighed about 265 lbs.

Of course with 300 lbs of snow plow up front I don't think henrydes will want an additional 265 up there!

Agreed Wes, the plow is plenty of weight. A lot of that weight hangs onto the front frame horns so you certainly do not want to stress them more. Sandbags in the bed may put a bit more power to the rear wheels.
I plow with a 65 CJ5 and the tire slip is better than broken frames, axles and ujoints. It will move 18" without too much stress.