Gt40 e303 combo questions

All purely my opinion based on my old 306 and all the dumb stuff I did on the way to basically this list:

70mm Accufab, 80mm MAF from a 1996-2000 (no integrated IAC), minimum of 3.5" cold air kit from filter to throttle body, 30 lb/hr injectors, and get it retuned. If you have not replaced the fuel pump then go with a 190lph Walbro or the like.

Your stock TB is 58mm and the MAF is a 70mm so the 70mm TB and 80mm MAF will definitely help with your combo. No reason not to get the 30 lb/hr injectors as they do not cost anymore and give you a lot more room so you are not running past 85% duty cycle. You get past that and the idle starts to suffer and your tuner will get frustrated.

The questions is more about what else are you looking to do after the MAF/TB change?

My set up is 90 GT with GT40 3 bars and unported EGR type Explorer intakes. I have a Crower 15512 cam (similar lift to an e303) and 1.7 roller rockers. I have a 70mm TB and EGR spacer, but have run this with a modified Explorer 65mm TB and it worked fine. I have run this combo with both a C&L 73mm MAF with Explorer 19s and a 76mm MAF with 24s. I have MAC equal length shorties, a catted 2.5 Pro Chamber and 2.5 MAC mufflers.

As AeroCoupe said, you don't want to continuously run over 85% duty cycle. Saying that I found when I was running the 19s I only ever reached or exceeded 85% at greater than 5000rpm and usually only a second or two at a time. So unless you are planning to be running at 5000 rpm and higher for extended amounts of time a good set of 19s will work fine and will give better drivability. I did change to 24s for the duty cycle reason (only because I had the parts and could as opposed to feeling the need). I have a dual wideband gauge and with the 19s I NEVER saw readings that would concern me when I was exceeding 85% duty cycle.

I would recommend a 65 or 70mm TB, keep your stock MAF (as a 70mm MAF will flow more than enough air for a 302 at RPMs less than 6000) and enjoy. If you plan power adders, that changes the whole thing. But if you are just looking for a fun driver, that would be the simplest and a slight upgrade from what you have. With a TB change only I would bet you don't even need a retune (the MAF reading in the tune will already tell the ECU how much air is going into the engine so fueling should be fine).

Just my two cents.