Okay I think I’ve figured out the confusion on the head for this motor. From the picture you have a 55 Johnson with an Evinrude powerhead. The block you have was in use for Johnson/ Evinrude between 51-56, rd11 though rd18, which started as a 25hp block and I am unsure what changes were made but the same block was used on the 56 30hp.
Since the Evinrude block you have has a Welsh Plug, that powerhead came from a 55 Evinrude 25, the first year 25hps had that Welsh plug with the serial number stamped in it.
Now, I have four 54 Johnson RDE-16’s which has a very similar head as the one you stripped.
I have a 53 Johnson rd-15 which has another head that is pictured below
I have four of the 55 Johnson RDE-17’s which has the same head as the online picture you found and the one on Outboard Nut’s 55 25hp.
I have 2 54 Evinrude’s with the same head you stripped.
Thus between 53-56 there were three different heads heads in use, why? Maybe due to casting difficulty or better design but notably look at the castings where the cowling attaches, they changed to accept the new flip up hoods in 55 though still had the casting bosses to be tapped for a pre 55 cover.
According to my books:
1953 rd-15 head part #: 375779
1954 rd-16 head part #: 376336
1955 rd-17 head part #: 376336
1956 rd-18 head part #: 277419
I have the head you’re looking for but it has a stripped hole as well. Send me a PM and I’ll keep digging, I know I have the one you’re looking for somewhere. Hopefully this helped.
P.S. if you can’t tell I like the 25hp rd’s 🙂
