1991 gmc k1500 my new toy/work commuter

[CrazyAsianR6]

So im new to truck community as I own a 95 toyota supra. But I know my way around a wrench and google
I have a few questions and hopefully some knowledgeable sierra owners will know the answers

Here is my truck. Now this is what it looked like when I bought it. Exterior was ok. Inside not so good. And engine was described as a v6 as did running the vin #. Well surprise surprise there's a v8/350 in there.
Now my problems with this truck are I have no turn signals but my hazards work and brake lights work.
Ive changed all fuse plugs, flasher relay. Turn signal relay. Replaced every bulb outside of truck and inside the dash. Still no go on blinkers. Now im wondering if it's the metal connector piece behind the steering wheel that might be the problem. Any other ideas or am I on the right track as well as out of options afterwards?

Next problem. Minute, but I pulled the grill off and painted it. While looking online for ideas. I couldn't find a 91 with this style of grill. Or these halogen big ass square headlights. Is this from a different year? Im trying to replace the headlights with something newer but I need to know the year so I can order one that will fit the big square hole unlike the rectangle shaped ones on every other model I've searched.

 

[CrazyAsianR6]

Lot of viewers. And no replies. Not even a welcome to the forums. Not quite as friendly and talkative as supraforums. But im still working on this truck everyday.
I just laid down the wire work since one of the last owners installed a bunch of kc off road lights in the front and rear. Only to find out all the bulbs are out. And naturally all the screws are stripped. So about to pull and replace them with some LED ones. Also replacing the stock headlamps with some projector halo headlamps. And replacing the running lights with LED bars, as well as tail lights and a LED strip 3rd bar under the tailgate with turn signal integration.
While working on the engine. I changed the oil and let it run hard for a little while before cutting open the oil filter and dumping that new oil to inspect and properly clear the inside of the motor. I thought that this motor was the 350. Someone else said it seemed smaller like the 305. But when I checked the previous oil filter on there I couldn't find a matching number compatible for those 2 motors. The only motor that used that oil filter was from a '99 gmc 454.
Can anyone please confirm from visual that this is a 454 block. Or where the blocks serial number is located on it so I can find it and look it up.

 

[CrazyAsianR6]

Is there a website that or maybe Chevy/gmc dealerships can look up engine serial numbers?

 

[Halftrack]

Get a chilton's General motors chevy gmc full size truck 1988-93 book. The serial # will give you all the info you need.
isbn#0-8019-8491-2