Find 90-91 Suburban cluster case that had a clock in lower LH where new fuel gauge needs to go. Easy way to do it or just hole saw in your original case. The case has the area to be cut molded into it.
I can't remember how speedo comes out. Been awhile since I opened a 90-91 cluster up but if I recall it's straight forward. Should just come out after screws are out.
This is NOT one you want but you at least you can see the hole the clock uses.
https://www.ebay.com/itm/1981-87-Chevy-GMC-Truck-Suburban-81-1989-K5-Blazer-Jimmy-Gauge-Cluster-Housing/202582026775?hash=item2f2ad46a17:g
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