i know a fair amount about these trucks.
first lets figure out what you disconnected. the hitachie carb needs many of the things connected to it and are not just emissions. besides removing emission stuff really just ****s up the enironment and will not help performance in anyway. The egr could possibly cool down over all temp but thats about it. the stock things on every engine are desiged to work together so they are all needed. There are some ****ed up emission **** on there that you can remove though but only if you have a weird model truck. like the the ones for high altitude have stuff thats uneeded if your not at a high altitude. i say put everything back together and then see if that solves some problems.
yes you can get a weber and they are easy to put on. if you want crazy hp/trq gain go with the 38
nis720 told me that he beat a 5.0l mustang and broke motor mounts because thats how insain the hp/trq gain was. even if the mustang thing is untrue the gain is alot with these carbs for sure but he also told me he was getting 10mpg, OUCH!
the option i plan to use is putting on this carb.
great gain and if tuned right you will receive higher mpg.
here is what alot of people do.
if your engine has many miles on it then do a rebuild. this alone with gain you added power if the engine is old and warn out. also change tranny and diff fluid. when rebuilding it its your choice to shave the head or bore it out. this will lower mpg though.
always do exhaust before large intake modifications such as a weber. dough thorly makes a good header also i hear the headers on 4x4parts.com are really good and way cheaper then a dough thorly.then exhaust should be about 2.2inch to either no cat or a highflow one then your choice of muffler or be a ricer a straight pipe it.
then add the webbber of your choice. or if you want **** gas milage add mikuni side draft carbs. these carbs with blow your socks off if tuned right.
make sure your cooling system is working well (before carb).then get and electric fan. I hear the 16inch S-blade style cools the best.
after this you can get the HB223B rear end and add an LSD for good traction. or just weld your diff. i would also switch to a single drive shaft.
as for your tranny problem. you either get a really exspensive rebuild or do the 280zx tranny. many other transmissions bolt to the z24. the zx tranny is less common and i know the 240sx (single cam) tranny bolts up also. all you need is the tranny (new clutch is a good idea also get a throwout bearing) and maybe a drive shaft.
ive seen so many different things done to these trucks so if you need more options just ask. you could always do a ka24e swap and gain a good amount from that also. even just stock.
any pics of what was disconected would help.
if you have more questions ask.