273 advise needed

If you only have 52,000 miles, your cam and lifters are probably OK. Your rings are probably stuck on the low cylinders. Change the oil to a good 10w-30 synthetic oil and a good filter. The AFB carb is not correct. Adjust the valves. Replace the freeze plugs with brass ones. Replace the front and rear main seals. Replace the oil pan gasket and inspect everything while you are in there. Can you get it running?