Good job with the chassis, my welding skills would not be up to that standard
NOS valve tappets are available , the cam looks almost new .
The general consensus is the Ford blocks are somewhat weaker with thinner walls in some areas. Quite common to see a crack below the dissy mount . I've not seen this problem myself, maybe its due to the colder climates of the Northern hemisphere where coolant freezing is an issue. Not much chance of that here with temps of around 30C the past week or so .