You have consiterable blow by on your 1991 ford 302 is there any additive that will help?

Not typically. Sometimes, if engine oil has not been changed regularly, you can run a cleaning additive with the oil and break loose some of the sludge that may be holding the rings from making a good seal in the cylinder. Typically that doesn't work so don't have too much expectation. It's usually caused by worn rings and the only solution is to rebuild the engine.