What Main Bearings do i use ?

I am putting a 49 up merc crank in my 1948,what main brgs do i use? i have a set(must be from a 49) because the thrust bearing will not fit the block,the are federal mogul 646m. i guess that i have to use main bearings from a 1948 , and they will work with to 49 crank??Thanks Randy

 

Use the '48 mains, use rod bearings to suit whichever rods you have.

 

Don't forget to check for clearances, 239 blocks need to be "opened up" a bit to fit a Merc crank. Also the oil pickup tube will hit the crank.