if the compression is good and head is redone or its also in atleast 85% in its condition ... it will be a blessing to check out synthetic as it will clean out all the pulp and carbon which has been accumulated like cholesterol in it ... but if the engine is already half they way wore out that it will make the situation worse as it will clean it and open more opportunities to penetrate deep and getting into firing chamber... for Old thumpers most of the time I have read that mineral Oil usually thick increases its life... so it merely depends on your engine condition.
