1985 GMC C2500 (New to me)

[wackypez]

Hello,
I just recently purchased a pretty clean 1985 GMC C2500, it runs good and the body is straight with recent paint, except a faded hood it looks great. Its solid but I can't leave well enough alone and come seeking advice on upgrades and modification. I’m not really concerned with the aesthetics yet mostly because it looks good and I want to keep it as period correct, as convenience will allow, I intend to use it. I have briefly researched some upgrades I want to perform and would like your feedback about whether they are worth while and what order I should go about it?

Pertinent info = 1985 Sierra classic, 350, TH-350, 4:10.

As purchased mods = Flamethrower HEI, Relocated intake to draw off grill, Bullet exhaust "cat" back system (I had to have a cat installed as it would not pass smog without it and the high flow model made no noticeable difference in current output and drastically dropped my emissions which gives me alot of room to play with mods and still be legal here in California).

Planned mods
1. K&N filter (what kind do you recommend? keep stock box or open element?
2. Tachometer, any recommendations?
3. Flex-A-Lite 295 Electric fan ( my fan clutch always seems on )
4. Edelbrock CARB legal shorty headers

This is where I get undecided, should I wait till engine shows fatigue (it may already and I just don’t know) and needs to be replaced or wait to upgrade it when/if I need to replace the engine? Either way I want to put the below on either a GM Goodwrench 350ci / 260hp (any other sane recommendations?) or the 22 year old 350ci / 190hp that appears to be solid right now.

Edelbrock Performer 600CFM carb
Edelbrock Performer manifold (Vortec)
Edelbrock Performer-Plus Camshaft Kit
GM Performance Parts Cast Iron Vortec SBC Heads

Any input on the transmission? I would like better gas mileage and highway cruising at a lower RPM but I have the TH-350 is a decent transmission?

Thanks