I have an early car 5.7 in a 71 Demon. TTI headers and biscuit mounts.
I had no modifications to the headers. I did modify the engine mount and bracket to clear a 90 degree oil filter adapter.
Modified the K member for oil filter clearance and made the engine mount slot holes longer.
I reused the stock pan gasket with the Milidon pan, no issues.
The pan to K member was too close, so I modified the K member so the pan can be easily removed.