on a 91 GT convertible auto with 327 gears - “ IF “ I needed ( or wanted ,lol ) the top half engine rebuilt ( I know the term rebuilt is vague ) say a head gasket failed and needed to put a lot of labor hours in it . AND , I wanted to stay some what stock but get some extra HP power and torque from the effort . Does this sound like the way to go if head gasket change needed : retain the original iron heads ( more durable to resist warping ) have machine shop port them , change valves , guides , springs and add 1.7 rockers & port match the lower intake , then add some equal length shorties . Would this add some power ? Would stock throttle body , injectors and upper plenum be sufficient ?
Yes it would add 'some' power.
Is it worth it dollars and cents wise? I don't think so.
This is what I would do: fix the head gasket. Have the heads checked, maybe a valve job if needed. Add a set of ceramic coated headers, stick a set of 3.73 gears in it and drive it.
Optional: if you can get a set of explorer heads that are good and cheap +1, explorer upper and lower +2. Keep all the rest stock.
DISCLAIMER: Just my opinion and not based on any real world mechanical experience.
The stock heads are no way to make HP cheaply. I'm not even certain that I would do headers on the stock pieces.
There's no way around the initial investment. If you want to make a noticeable difference in HP, you're going to have to either heads and supporting mods or invest in a blower.
You didn't mention miles but either option also includes supporting mods and a thorough examination of all the soft parts (gaskets, seals, hoses, etc... (for those that can't imagine what I mean by 'soft parts')).
...and don't even [think] of adding more power without sub-frame connectors and completely revitalizing (perhaps upgrade) the brake system.
A 3G alternator upgrade is [highly] recommended just to ensure coil saturation and the larger fuel pump (not to mention any other electrically demanding upgrades).
I mentioned the ceramic coated headers mostly for looks, those stock headers are fugly!
If you look at ads for aftermarket heads they claim big gains but if you look at the dyno results they use fresh engines and no accessories. Search the motor trend channel for sbf dyno stuff, Jeff Smith thrashes some stuff that will surprise you with the results.
Again money spent on port and polished stock heads are better spent elsewhere.
It is very unlikely that the stock heads gasket will ever just, "Go". They are iron heads, mated to an iron block, and unless you plan on detonating or overheating the entire combo, the head gaskets will probably outlive you.
When I pulled my nearly 200k OEM motor out from under the 2.2L Blowzilla, they looked just fine.
Oil pan, rear main seal, and valve cover gaskets were a different story.
My point was, if you are going to spend the money, take the money you would have spent on redoing stock heads and buy a good Aluminum cylinder head and base your combo around that. You can use an explorer intake, off the shelf used cam, etc...but pick a good foundation to start with.
I was considering gears -it has 327 factory option gears , but I agree higher ones would be fun - I use the car as a daily commuter and live in area with speed cameras every mile or so ( $130 gift mailed to you for going over limit 11mph - most roads are 30mph .... ) I enjoy simply cruising in the car with top down - rpm at 1800 on highway 60 mph .
I like your thinking General ! Cleaned out the fins on radiator yesterday , going to flush old fluid out today and see how it does - maybe I will get lucky and drop temps down 10 degrees or more and call it a day .