Hi I have an old never used OS 50 max but it's missing one head bolt. There are suppose to be 3-long head bolts and 3-short head bolts with one of the short ones missing. Is there any substitution bolt for this engine or am I going to have to hunt one down. Or should I just drill the hole out bigger and used a different bolt. Here's some pics of the engine. I believe its from the early 70's.