An easy filter fix is one of the metal filters commonly found in your local auto parts emporium. I would mount it near the fuel pump outlet so it would be below the exhaust manifold in the remote chance it developed a leak.
Here is your first purchase!!!
https://www.rockauto.com/en/moreinfo.php?pk=10593924&cc=1486874&pt=10335&jsn=382
Rock Auto has the head gasket:
https://www.rockauto.com/en/moreinfo.php?pk=121713&cc=1349917&pt=5412&jsn=416
Also your friendly NAPA can help you out:
https://www.napaonline.com/en/p/FPGHS7564C
These flatties were produced in various flavors up to about 1970, often used in fork lifts, farm equipment, stationary pumps, etc. Check the mainstream suppliers first then you can use the specialty vendors when necessary.