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In a recent rodding magazine, they showed a rebuild of a flathead FQRD. The pistons had an extra oil ring below the wrist pin. Is this a common performance design?

Also, in the same issue, the cylinders were being bored out using a jig that was also attached to the main bearing supports in the block. Is this a common method or is it fairly exostic ?

The extra ring or rings was common on vintage engines, especially ones with oil control problems or extremely long skirts. The trend since the 40's has been 3 rings with the rings becoming more narrow.
I didn't see the article, but the jig is most likely a torque plate.It gets bolted down to distort the block the same as when it's fully assembled or it may be something associated with boring Flathead V-8's Torque plates are often used when boring engines , most are bolted to the top of the block to simulate head bolt stress.

Tony,
I found the article again and it is in the June 2003, Rod and custom. The setup uses a "half circle saddle that fits perfectly in the mains, ensuring that the bore is exactly 90 deg. to the block". They also used the main bearing jounals in the setup for machining the three top surfaces.

Want to make a Chevy fast? Put a GMC in it.

Two oil rings are no substitute for proper piston design.....more rins more drag=less HP
NO NO You can't run em without rings!!!Chevy Guys

Tony, have you had a look at the pistons in the latest super sport motorcycles? In order live within the limits of piston speed they have gone to extremely oversquare designs to get a 12-14000 red line. To minimize reciprocating weight the pistons are no more than what it takes to support the wristpin and three rings - ain't no piston skirt hanging below the wrist pin. They are all using intricate oil passages ending in nozzles that spray the underside of the piston to aid cooling with overspray catching the cylinder wall.