Hi Alan,
I don't have experience with the M/T DOT radials specifically, so this is just a general opinion.
The RMA (Rubber manufacturers association) recommends 6 years on passenger car tires. This has always seemed a little aggressive IMO, and besides- they represent companies who sell tires. However, I have become more cautious and start thinking about 8-10 years certainly.
It has also been my observation that generally, race compounds deteriorate somewhat faster. I think UV/Ozone exposure is partly to blame, so storing them inside may have reduced that effect.
I think it's a good question, but in the end... Making a 100 MPH+ pass in a valuable vintage car... It's your call, but honestly, I would be having negative thoughts if it were me.
BTW I have a pair of BFG Drag Radials over 20 years old. I wouldn't do more than idle around the block on them to blow the cobwebs out. If that.