310 diesel engine in a 1550 diesel

Any 7-main block (283/310) will fit, but it takes some elbow grease to do it. Others have mentioned the bellhousing tricks and such, but don't forget about the front of the engine either. The 7-main blocks have a higher deck height than the big brother 4-main block (88's for example), and both of these have higher decks than your 1550 block. The problem with the 1550 is that it never grew up. It uses the same bore centers and block length as the 77. Also the cylinder heads from the 77 to the 1555 were relatively the same---meaning poor flow and no options to upgrade. What this all means is that the water pump sits higher on the 7-main block engines so you'll need to go to a smaller fan. In my opinion, if you are going through that effort, either put a windmill on the diesel or go gas. A diesel without a windmill is useless in the pulling world. The 310 diesel head flows okay stock, but you can hit 100HP with a 310 gas with a 12 port head stock (2600RPM). Good luck with your project.