… But all that is just theory. The main difference between the STC process and the Field Approval is the STC is reviewed by the Aircraft Certification Office (ACO) rather than the FSDO. But, in reality, if the FSDO considers your Field Approval modification a bit too complex for them to vet, they most likely will kick it over to the ACO and now were talking 1-time STC.
Clear as mud, right ?
But back to the OP:
If you wanna go fast & efficient, sell the TB20 and get yerself a Lancair/Columbia/Ttx 
Over the years I have seen countless FAA docs listing which installations need an STC, but whether they have absolute regulatory force I don’t know.
I don’t see flash rivet replacement as easy since you need to dimple the upper skin and countersink the lower skin, which means taking apart the entire aircraft. But it’s an interesting mental exercise – the sort of thing I like
If I wanted a Lancair IV I would have one already. All these homebuilts are useless to me in Europe because they can’t do legal IFR in most places. The TTX is good but it has the wrong sort of landing gear 
Anyway I don’t want to digress.
Peter wrote:
But it’s an interesting mental exercise
It’s a “metal” exercise to be sure
