I have a 1984 150 V6 Johnson (J150TLCRD) which runs well, but I would like to bolt on some additional HP.

I picked up an Evinrude 150 GT powerhead (E150STLCOS).

Some questions, my understanding is that the blocks and pistons between these engines are the same. Is this correct?

Differences lie in the carburetors, reeds, heads and alternator circuit. Are there other differences?

The 150 GT powerhead has a bad hole, so I am planning on swapping over the carbs, reeds and heads. I don't need the additional alternator output.

What I find odd is that my straight 150 has a high speed timing value of 26 degrees BTC, but the intake cover on the GT calls for 34 degrees BTC? Does this sound right? If so, why so much difference? Does it make sense to increase the timing to 34 BTC on my straight 150 engine once I change over the heads, carbs and reeds (actually will be installing Boyesen reeds)?

Larry S.