Pulling the heads will accomplish nothing for you except doing a lot more work, costing you more money for gaskets/bolts, and giving you more possibility of blowing head gaskets. (if the new ones don't seal right or something) Basically, the rockers you just pull the front valve cover off and replace those, IIRC there is nothing in the way preventing you to do this on the bonnies. (on the w-bodies there is an engine mount in the way) On the rear however, you will have to remove a few things, the alternator has to come off, obviously the belts, the bracket for the alternator covers up the valve cover a little and you will have to loosen that up a little to pull it out of the way, and there are a couple brackets with sensors on them in the way as well. So you just unbolt that stuff (should be pretty obvious what needs to be removed while your in there) and take the rear cover off.
For springs, the easiest way IMO is to pull the spark plug on that cylinder and connect an air hose to it to compress the cylinder with air so the valve doesn't fall in. However, if you don't have access to an air compressor then throw that idea out. There are other ways to do it that aren't too bad as well, and I'm sure others will chime in on how to do this if you need it. If you are doing headers at the same time this is the perfect opportunity to put them on when you have stuff removed and there is more room.
If you are doing a cam, put the headers on when you have the intake manifold, supercharger, etc... pulled off because you will be able to get at them much easier. Don't pull the engine, and you don't even have to drop the cradle if you don't want. What I do, because it seems a lot easier IMO, is I just drill a hole in the fenderwell that lines up with the cam and pull the cam out through the fenderwell. Then, after you slide the new cam in and button the engine up, what I do is I put a plate covering up the hole in the engine bay and I rivet it in, and then in the wheelwell I take that rubberized undercoating and spray it in there and it should match your wheelwell pretty well and it won't look too bad.
And, just to clear things up, you can't install rockers and a cam because you will have too much lift. You probably already know this, I just want to make sure. Unless of course you're going with a mild cam and you want to run 1.7 rockers with it, although that usually requires some head work to be beneficial.
1990 Maroon Grand Prix STE McLaren 3.1 Intercooled Turbo, 14.695 @ 94.49 on 12psi before cam/heads/etc.
1990 Bright Red Grand Prix McLaren 3.1 Intercooled Turbo, 14.819 @ 92.72, 189whp
1999 Grand Prix GT 9.75:1|K&N|160 tstat|No Ubend/Cat/Res|UD Pulleys|Ported M90/TB/Heads|XPZ|2.55"|Pacesetters|Stage 2 I/C. 12.442 @ 112.78
2000 Blue Bonneville SSEi Supercharged Gutted Airbox|K&N|3.4"|1.9'*|WP Pulley|Custom DHP|180*stat|41932'*|No Cat. 14.681 @ 94.80
2002 Dark Cherry Grand Prix GTP Supercharged & Intercooled
12.084 @ 114.38 w/1.743 60', 315.6whp, Fastest Stock Cam M90 GTP!
NOW XP CAMMED, 340.6whp with XP, stock heads, Gen 3 M90, 11.984 @ 115.84 w/1.750 60'!
Most HP Stock Heads Gen 3 M90 GTP!
2004 Red Monte SS Supercharged K&N|3.4 Pulley|1.9'*|180*stat|41919 plugs|3" dp|No cat/ubend|DHP|Shift Kit. 14.2 @ 98
GOT BOOST??? Friends dont let friends drive stock!