They are M10-1.5x15m/m, as I recall. However, they are "place bolts," which have a special head design and use a somewhat different heat treat process than SAE Grade 8/ISO 12.9 to make them not so much "harder" as "tougher."
Use OEM, or get ARP bolts. I don't know if ARP has a part number that will work for us, but if you were referring to Flexplate bolts, there's a Pontiac kit that works well. Let me check...
OK - per ARP2005 (it's not a direct listing - sort of "cross-referencing...) I'd get ARP K/N 230-7305, which will give you six pcs M10-1.5x15m/m - a full set and two extras. This is a new part number for last year, just so you know... This kit is listed for THM200, THM700R4, 4L60, & 4L80 with six-screw metric converters...
5-90