It does help to know the actual width of the tires for mocking up and calculations. Every manufacturer is different. When I purchased my 315s I was referencing most of the big name brand sites with good luck finding their measured widths. I ended up with Nitto NT-01.
I found that 0 offset barely cleared the 315/30R18 on my Blazer, so you could actually be fine there. 2.5" = 63.5mm, so you're at -4.5 offset. S10 frame width is nearly identical to the widest portion of the Blazer in that region FYI.
Up front 275/35R18 shouldn't be too far off. My 275/40R17s rub a bit, but have plenty of steering angle. Your spacing is out 5.5mm from my 0 offset Cragers, so that is improved too. Also remember that while out on the track or tearing it up around street corners the steering angle is not approaching the max. It is only parking lot or low speed maneuvers that will max out. If you're fine with reduced convenience front tire width becomes less of a problem. Rebuild the steering stops or just learn how far you can go.