Was it running with automatic oil injection ?------Did you install a new water pump impeller about every 3 years ?-----A replacement power head is the best option.----But find out what happened and make the repairs.
Easy to convert---Remove 5" spacer.----Install shorter driveshaft.-----Install shorter shift rod.----Remove 5" water tube spacer or cut 5" off water tube.
Tools are not expensive.----Spark tester is easy to make with wire , glue and cardboard.---You need to provide information.-----No one on the forum can touch your motor.
With a bit of fuel in the cylinders it should have roared like a wild lion.----Does spark jump a gap of at least 3/8" , yes or no ?----What are the actual compression values ?
Once again this depends on what gearcase is fitted on your motor.-----It could be a newer gearcase or older gearcase.-----Or even a V-6 gearcase.----Pictures , pictures can help you get the answers you are seeking !!
??---A strong 1/8" could really not happen.----Motor would have quit long before that.---The cylinder head was warped.----Did you refinish it before installing the new head gasket?