If you have the ability to measure the holes in the bellhousing and back plate through which the bolts pass, you'll notice that two measure a bit smaller than the others... they measure right around 0.375", if memory serves, while the others are like the next drill size up... like 13/32" or something.
Looking at the transmission from the REAR of the car, the two smaller holes for dowel bolts should be at the 11 o'clock position and then about 180 degrees from that at the 5 o'clock position. So on top, it's the hole opposite the one that threads into the engine block, and then 180 degrees from that one, under where the starter mounts.
FYI, for you or others, I ended up just using AN176 aircraft bolts in these holes, which are basically exactly what the original "dowel bolts" were (was missing one of my original dowel bolts). They cost me like $0.50 each.
Regards,
Robert