MC-1 to Alpha One Conversion

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chcknben8

Recruit
Joined
Aug 27, 2025
Messages
1
Hope all is well with everybody, I have recently joined the boat community and bought a 74 thunderbird tri-hull. The 120hp merc was seized and the mc-1 outdrive and gimble was in pretty rough shape, ripped everything out and transom is solid. I recently purchased a alpha one gimble, outdrive, and inner transom assembly, and pump and was wondering if this will bolt up to the same mounting bolts as the MC-1 or if I have to drill new holes. Also, I would like to find a motor for this boat also but am hesitant on major modifications. What engines would basically be "plug and play" in place of my 120hp merc?
 
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Pmt133

Ensign
Joined
Jan 6, 2022
Messages
977
I think there are some differences in the holes for the transom. Not 100% sure.

As far as engines... 3.0l/120/140 from the 80s up would be more or less drop in minus some alignment once the alpha assembly is mounted and possibly a longer throttle cable. Maybe have to get creative with the electrical... my 3.0l had a different plug than the 140 it replaced.
 
redneck joe

redneck joe

Supreme Mariner
Joined
Mar 18, 2009
Messages
12,712
I cannot provide detail because I paid someone to do mine but it is doable. No difference in transom hole afaik
 
Alumarine

Alumarine

Captain
Joined
Feb 22, 2005
Messages
3,755
What was the original motor that was attached to the alpha 1 outdrive?
It would be best if it was from a 120/140/3.0 so the gear ratio would be correct.
 
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Pmt133

Ensign
Joined
Jan 6, 2022
Messages
977
Yeah I'm not exactly sure but I think sometime between the early and late versions the hole spacing changed. I do know there are 2 versions of the cork gasket with different spacing and I think that is earlier 70s. At some point it switched to the foam strip same as the MR, alpha etc. That if in place should be the same but that would be later 70s.
 
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