Installing autometer tach or speedo into stock cluster?

[LincoConti87]

I'm wondering if anyone has ever tried to just cut out a round hole in a stock 87-93 style cluster and say put an autometer 5 inch tach or at least a 3 5/8s tach because the stock tach is just horribly off from everything I hear and it looks way off. I dont wanna spend 450$ on a florida5.0 cluster setup and they dont look all that great anyways. Why can't it be done?Someone mentioned that the speedo and tach when pulled out produce square holes in the cluster but then why can't I just make a plastic trim piece with a round hole?

Am I wrong or have people even installed 160 and higher speedos out of SN95 cars in fox body's? Ideally I'd like something like a 160 Autometer speedo and 8000rpm Autometer tach to match