1999 6.5l non-turbo engine number: 12555508
Can anyone cross this number to see what it comes out to be? Is this the navistar block number with the advanced casting?

As far as I know, there isn't a 508 block, scrape off some more of the grime off the back of the engine to see if it's a 506 block. To tell if it's the updated block you'll find a diamond logo casted onto the block.

The thing is, this motor can be gotten for a great price. It is out of a big box van with low miles and it was pulled for warrenty due to a head gasket leak. Well, I have two new heads on my blown 98 that would feel right at home on this engine. The dude said it is a 1999 motor Non-turbo which should not matter, right? All the same stuff inside as my 98 TD. I am just confused as the numbers. Maybe I will see my local GM service nut-balls for an info sheet.

I was wondering how to tell what block I have. According the info in red (below). Would that mean that I have a "641" block? I recieved this information from a VIN check from the dealer.
Chad

Repair Order Date : 08/16/1999 Repair Order Number : 135699 Odometer Reading : 21580 miles
Serviced By : THOMAS PONTIAC, BUICK, GMC, INC.
3350 129TH AVE NW


COON RAPIDS, MN 55448-1020
(763) 323-3333 Selling Source : 48 - GMC TRUCK
Site Code : 14025
Business Associate Code : 116233
Cycle Date Cycle Nbr Case Type Labor Operation Part Auth Code Person Code Line Total Comments
08/31/1999 990 01 # J1840 - ENGINE, UNIVERSAL - REPLACE 12457641 EP N/A $ 6924.37 N
08/31/1999 990 02 # C6871 - COVER AND/OR PAD, FRONT SEAT CUSHION - LEFT - R&R OR REPLA N/A P N/A $ 32.00 N
08/31/1999 990 03 # Z7903 - 3-DAY COURTESY TRANSPORTATION N/A N/A N/A $ 90.00 N