I have a sm645 transmission off of a 79 k10 on a Chevy 230 straight six off of a 65 c10 but I don’t have a starter that fits. And I tried looking one up but I’m not sure what I should be looking for. Would a starter off a k10 4 speed with a v8 work or does it need to be one for a straight 6? Or someone could just recommend me a starter they know will bolt on and work for my stuff that would be nice too. Anything helps thank you!

 

The Muncie SM645 wasn't in use by GM until 1969 in a C-10:

https://en.wikipedia.org/wiki/Muncie_SM465_transmission

Muncie's were good transmissions, but both the Borg-Warner was as good or better. Both 4 speeds with a Granny Low 1st gear. No Three on the tree shifter. By 1969 the 250 and 292 I-6 replaced the 230 I-6. It might be possible that a starter for the 250 I-6 and 465 Muncie tranny starter will work, but I can't say for sure. I 'did have an idiot friend, who jumped ditches with his fathers 1967 C-10, but it held up well, but they burned up the motor and put a 235 I-6 motor due to neglect and his treating everyone's car or pickup like crap. His brother ran his motor oil changes up past 50,000 in a Fe'd up Beyond Repair vehicle. When he tried to trade it after 5 years he got pennies on the dollar for the P-O-S. The motor was running but that all. Back the carb would flood out with stuck floats or if you took a trip up the Rockies, they turned very rich, and some wouldn't make it at all. They had to be tuned for high altitudes, but if new the factories would tune them for that.

The only other thing would be to rebuild your current starter, or modify a rebuilt one. I had to have that done with my father 1969 366 large Block V8 C-60 2.5 Ton medium duty truck, when I ripped everything off the top end including the SMOG PUMP, which ended up in a ditch after my .357 Magnum got done putting 6 holes in it, as I was pissed off as it was not required by law and was about the 7th or 8th one that the dust chewed them up. New Holley 650 CFM carburetor too, but I wanted a vacuum advance distributor, so with some modifications, that is exactly what I had, Power and gas mileage went up too by a lot.5-5.5 up to 7MPG plus on gasoline use.Later on I put electronic ignition in it too, and no more changing points every month......EVER AGAIN!!

More searching the Internet might be wise. You might find a starter on eBay too.