307 Regal, The T type package makes that a nice regal and the 87 is often said to be the best looking. Light good looking 15x7 wheels, quicker ratio steering box, stiffer springs and the bigger front sway bar plus rear sway bar make it much better than a standard regal or gbody. Ditto on regular radial tires. Long burnouts often make them greasy. Don't put money into performance parts for that 307 as their is little bang for the buck in it. Just run it while you build something else. If maintained and not abused the 307 usually lasts over 200,000 miles though. Do look at your suspension end links as they often have missing or mushy worn out rubber. Good polyurethane end links are cheap and easy to replace for an often noticeable cornering or handling improvement.
On your transmission you might at least add a good shift kit like the ones that
http://www.ckperformance.com sells. I bought one from them for $100 on a special. Firm quick upshifts even at part throttle but not harsh like some. Cheap B&M etc kits won't work well on this trans. It might be good for a tenth but mostly it will help your transmission live. Nobody wants to do a rebuild before its time.
http://www.extremeautomatics.com built two 200-4Rs for me one in my GN after 125,000 hard miles and one for my 575 foot pound of torque 509 powered 442. Both have held up well. FYI here is what Extreme Automatics has to say about the 700-R4.
Q - 2004R or 700R4?
A - I have been asked this question more than any other. Straight answer some will not like. Honestly its not even a fair fight. The 2004R will handle power that far exceeds that of any 700R4 or 4L60 that can be build at any price. 2004R has a better gear ratio spread, better Overdrive ratio, will fit many more applications, Lighter, Stronger I can go on and on. The 700R4 is best left to applications where its the only option such as 4WD or All WD, tow vehicles, Lower HP applications or customers that are more concerned with budget v/s strength and reliability.
To clarify he means built to built transmissions as a 700-R4 is a little stronger than a generic 200-4R. Plus about the same money to rebuilt and no need to have a driveshaft shaft cut to make one work in a your car.