1979 Royal Sierra Questions

Crazyone · November 21, 2023

My grandson turns 16 today and should pass his driver's test tomorrow. His father, my son, bought a 1979 Royal Sierra for my grandson to drive as his first vehicle. It's a K15 4X4 that's been bandaged together over the years. I got the dealer invoice from the GM Heritage Center and that confirmed it was a real Royal. I do have a couple of questions and hope someone might be able to share for information that would help.

The first question is about the drive train. The truck originally has a 400 small block, currently it has a 383 stroker that someone put in. The RPO code for the transmission is listed as MX1 which is a 3 speed automatic. Other information that GMHC sent me list both TH350 and TH400 transmissions as being available but only the one RPO code that doesn't differentiate between the two transmissions. I'm wondering which transmission would have been originally in the truck given the larger displacement engine. Was the TH400 reserved for only the big block motors?

My second question is about the VIN location. The documentation indicates that for 1979 the VIN should be visible through the windshield on the front edge of the dash in front of the driver. This truck is not equipped that way, nor is there any other VIN plate to be found. The truck has been repainted and the glove box door does not have a sticker that matches the title VIN number. My question is whether or not the VIN relocation to the dash was a clean model year break or did GM use up existing stock built prior to the changeover? Is it possible to just change out the dash?

Any insight would be greatly appreciated.

newdude · November 27, 2023

Turbo 350 should be RPO code MX1. Turbo 400 should be M40 but looking in the 1979 Chevy model guide for example it shows "MX1" 3 speed automatic but then in the data page for the transmission it shows all of the 3 speed auto transmissions they had. Same for the ordering guide just shows "MX1".

I'd imagine the 400 was used in C/K 20 and 30 trucks with small and big block V8, possibly the high power inline 6s? but I could be wrong. A 10 series probably all THM 350 unless its a 400 engine?

Here's the link I was talking about: 1979-Chevrolet-Truck.pdf (gm.com)

VIN, I'm not sure but per here - 1979 - 1980 CHEVROLET TRUCK VIN NUMBER DESIGNATIONS - Vehicle Identification Numbers decoded and deciphered - Chuck's Chevy Truck Pages (chuckschevytruckpages.com)

It should be the driver's corner of the windshield but not a 17 digit VIN for 1979-1980. 1981 and up are 17 digit.