Hi again, Awf!
Yes, the chamber reamer and sizing die adaptation I suggested is gonna be a compromise. You didn't want to buy or rent reamers, remember?
Yes, cutting off 0.500" from the sizing die, making your trial .308x1.5" cases, and then short-chambering using a standard .308 Win reamer to produce a chamber that will headspace those cases correctly MIGHT give you tight chambering issues. I would start with the RCBS "small base" sizing dies, and then experiment with several brands of cases to see which is the least work.
If you really are looking for match quality results, you probably won't get there easily without custom chamber reamer and reloading dies. RCBS and Redding (among others) offers them of course, but they are expensive.