Block-70 are only available new, latest upgrade standard is named F-16V (Viper).TAI does not have the expertise to upgrade to block 70 version. It would be performed in the US, unless PAF is able to push for a local upgrade at PAC, though that seems unlikely.
There is also little sense in upgrading really old airframes to the latest version, such as the Jordanian aircraft. If anything, upgrade just the latest block 52s and buy another squadron of new aircraft. Use the radars and other equipment to update the block 15ADFs to the same MLU standards basically as the current fleet.
That means any used aircraft could be early C/D variants or lower life (if any) block 15s. Looks like there are 201/37 A/B variants and 112/13 C/D variants in storage at the dessert, give or take.
I think even having a fleet of 45-60 block 70s, both upgraded and new, would be very potent and could lead the existing MLU birds in cooperative engagements. Don't think we need to or can afford to have every single aircraft upgraded.
Coupled with block IIIs, we are going to be in a very good position to work on AZM.
TAI is a licensed producer to Lockheed Martin, what they can do is get parts from LM in form kits and integrate on behalf of LM, same as was done with previous PAF jets. Logistically its simpler to fly the jets to Turkey rather than US.
Besides Turkey is working on its own domestic AESA radar and upgrades for its F-16s. This would need blessing of LM in the form of certification or will need to prepare disownment from LM for performance of the product. F-5 and F-4 upgrades from non manufacturers have been done in past. No idea on how TAI intends to finally implement it.
Under Biden I suspect Turkey will still be barred from F-35 and future tech but expect remaining cooperation to restore. This sill give India some relief from CAATSA on S-400 purchase as well.