You can get gaskets that have separate half moon pieces e.g. Durapro Oil Pan Sump Gasket suits Ford Falcon AU-AU III 4.0 Litre (SOHC 12 Valve | eBay
and Durapro Oil Pan Sump Gasket suits Ford Falcon AU-AU III (VCT Tickford) 4.0 Litre | eBay
so you could probably just use a half moon piece and cut the old gasket square at the joining point. You could also carefully cut the required piece from one of those continuous sump gaskets. Whatever you do just make sure you cut the mating point of the existing gasket squarely with sharp trimming knife (brand new blade) and apply sealant in the same way as where the timing cover meets the head per Figure 32a Section 82-2-18 of the factory workshop manual. My only major concern is that the cause could be that the harmonic balancer / crankshaft pulley may have been hammered on rather than using an installer tool at some point so the end play has been damaged to the point that crankshaft has excess movement and is pushing out the gasket (and perhaps causing some of the engine noise you had). If this is the case, ultimately, and sooner than you expect, the backward and forward movement of the crankshaft in the block will destroy the main bearing caps and cause other internal engine damage. I would be using a dial indicator to check the end play at the harmonic balancer end of the crank before going further. End play is usually checked with the engine out during engine assembly per section 8-1-11 of the workshop manual but you can do it in the car (albeit with some difficulty) following the method used at the start of this video and very gently levering on the pulley with a long screwdriver to move the crank:
Per Section 8-5-3 of the workshop manual the maximum crankshaft end play wear limit is 0.30 mm and normally should be between 0.10 and 0,20 mm.