What years of 225 will bolt into a 1964 D-100 pickup? I know it's a dumb question but I am new at this. thanks in advance!
P.S. more dumb questions to come.

Manual transmission or automatic?

The crank is the whole equation:

Any pre-1967 slant six will match your existing mill, if someone hadn't swapped in something else later in it's life.

The next thing to note is that if you have a Manual tranny and the donor motor had an automatic tranny mated to it, it may or may not have the pilot hole for your tranny input shaft (if the hole is there and it's unfinished, there are other options to make the swap).

-D.Idiot

It is a three speed manual transmission. I am looking for another engine to replace this one. and it is the original engine for sure. Thanks

I just finished sliding in a '85 block into my 64d100. Rob is right, be sure you read the available info from this forum re. crank input shaft holes. I'd advise a finished hole on the chance you might want to put in a 833 one day. In which case 9of adding the 833) the crossmember on which your NP435 3 speed sits, won't be used. Do you have the transmission parking brake or cable parking brake? The tranny with the drum brake has the so called "universal" bellhousing with the hips on it like a poly 318 block and weighs about 65 pounds and is a real pill to get off the back of the engine........at time of engine swap is a REAL good time to put in a new clutch whether or not you THINK you need one just now..
rock
'64d100

What is an 833?? thanks!!

A-833 = 4speed


-D.Idiot

Make that the passenger car 4-speed.

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Joshua