No aluminum model # plug on this powerhead.. Old 2 cylinder. How to identify??

[rebuilt]

I bought this plain powerhead years ago to repower a '73 18 hp fastwin. The man I bought it from was a fixture on this forum, but he passed some years ago. Tashasdaddy. We called him TD. I can't find any info anywhere on this block with any #'s. There is no plug with the familiar model # stamped on it. Right below the inspection plates, where the model # plug is on the shot '73 is a recessed plug. No #. The intake manifold shows a part # of 384201. BRP parts catalog shows this part was on a '69 something. Coulda been an 18, 20 or a 25 hp. Where on this block is a part #? I've looked and looked. Could use some help with this riddle. Thanks. Kevin

 

[F_R]

The main concern you should deal with is 18 or 20 hp OR a 25 hp.? 18 and 20 hps are pretty similar but there are significant differences in 25hp. I don't know that I could tell a 25 without tearing it down.

 

[rebuilt]

Thanks for your reply. That is my concern. What is the hp rating? It makes good compression as it is. A 1/2" drill chucked to a socket on the crank flywheel nut won't turn it over. I realize that's a silly compression rating, it's just for info. I was trying to get a compression #. It does spin freely with no plugs. I would hate to take it apart just to identify it. I'll put up some pics tomorrow.

 

[racerone]

Most parts have a 6 digit casting #.----What # do you find on the cylinder head?----What size is the carburetor opening where it fits on the intake ?---Any # on the upper carburetor body ?

 

[rebuilt]

The riddle continues. The only definitive thing I could find that BRP parts search recognizes is the intake #. It was used on 1969 models. 16 of them. I found two more #'s. One tucked into a recess under the thermostat housing on the head. Which is actually cast into the head itself, not the block. Very hard to make out. BRP does not recognize that #. I found another one on the intake side of the block. BRP doesn't recognize that one either. Both look just like a JE #. Same # of digits, start with a 3 in this case. BRP says no go. Change the last digit in the search engine and I get parts for a '69 18hp. Like the intake year. Just not the block or head. On these pics.... 383310 is on the intake side of the block.
306160 is in a recess on the head. 384201 is on the intake itself. It's the only one BRP recognizes. One other certainty. The carb opening is 1 and 7/16 inch, the way I read my tape. The little thing makes decent compression. I can only check it by putting a wrench on the crank nut and turning it by hand. It'll get 85 psi by hand. I can only spin it one stroke at a time. Sometimes it might go two. It's hard to hold. It fights back. I've got 6 more views. One from each side, one top, one bottom. Maybe next post. I can use thumbnails on that one.