I like the 334 or bored out 305 idea! Seriously. You must compare cost.
My worn out 305 with boltons and a 3:73 rear did a 14.7. You all can say whoopy but that engine had 165,000 miles and most newer stock stangs are in the 14`s! So with a cam and heads, with the puni 305 bored out.....that car can get low into the 13`s without a power adder. Be easy with that cam.
I would put in a Comp extreme 262 and a 600 cfm carb with that set up.
I believe the 6 inch rods will work. The reason you DO want the 6 inch rods is because you CAN run a higher Compression Ratio!! ..the higher the CR the more power you will have...because the piston will be dwelling a little longer when it is firing.
Don`t listen to the Bull**** you hear on the 305. You can make a 305 respectable...the problem is ...if you spend that much money on a 350, you will be 100 horsepower or soo higher.
Good Luck, keep us informed!