The telltales came out in 78. All the crossflow blocks up through 77 had the same powerhead bottom/exhaust adapter configuration. That bottom/exhaust adapter configuration changed in 78 when OMC went to the dual thermostat housing. Your powerhead has the single vernatherm thermostat, so it's no newer than a 77. The powerheads either side of that year are not interchangeable for that reason. Very likely the outer exhaust covers are interchangeable-maybe the prior owner just replaced the cover with a later model. Save all the drilling/tapping for the telltale hose barb. Easy to drill a hole in the lower cowling cover. Back in this timeframe, the powerheads were painted the same color as the rest of the engine. Looks like the powerhead was changed. If you don't have a serial tag on the transom bracket, look for a round casting disc on the top of the block-it will have the serial and model number....what does it say?
