72 C10 Cab Bushings

[GBJ]

I bought my 72 last April, 3 yr old frame off build with Vortec swap etc. I put aluminum heads a cam and headers in it before the holidays. We noticed the back cab bushings had a split in both. Last week I put a No Limit rear shock relocation kit on and the rear cab bushings were toast. I had already ordered new bushings from Brother's a few month's earlier. The bottom of the rear cab bushings were a two piece cup design I have never seen and don't see how they lasted this long. First pic is cup type bushing, second pic is front bushings and closer to what i got from Brother's. Anyone know what these might have been for?

Thanks