4 speed guys, I have a question :

Yes. You can tell by the sound of the short throw shifter. They usually had a 16-1/2 inch wheels and tire diameters of around 33 inches, hence the 4.88 gears. I’ve also seen 4.56 gears in the big block trucks. The geometric 435 transmission was typically in trucks with 4.10 or higher gearing, except for definite some slant six (I had a '73 D100 with 3.55 8-3/8 rear) trucks. I’m sure that you can find exceptions to that. There’s a fender type ID tag that will identify all your options (being the under hood sticker on yours is gone), but it’s underneath the cowl panel. A cell phone bore camera may get you a picture of it. I forgot that I did once have a '71 D100 parts truck that had a 3.23 8-3/4 and an NP445 in it, so they were'nt just a heavy duty only thing, but you usually saw more 435 transmissions in half tons.