Ah yes I go over this topic everytime I look at my truck lol.
Ok this isn't in any real order but to quote...
200-300 hp... Get back into the Ford/chevy relams.
Trying to keep weight balanced is tough with an 8 but possible choices for v6's would be Buick Grand National 3.8l, or a mildly done 4.3l Chev.
http://www.ultimatecustoms.com actually makes kits to convert our trucks to Ford and chev 8's and chev 6's.
The turbo 2.2 in the 626/mx6/probeGT will work in the b trucks. Same engine blocks with different heads. Using the whole motor is posible, and I think therte is somebody on this board that has done it. 145hp from the factory allthough many swear this number is underated.
The ultimate and likely most expensive swap is the RX7 rotary, 88 and up. Normally Aspirated, 165hp, Turbo 200hp, and if you got the cash and can find one 3rd gen Twin turbo at 255hp. There are people out there that can get 300-700+ hp outta these engines as well, but with the mega bucks too

Key thing with this swap being the near 50/50 wieght balance you can achieve which is good for handling and "go".
*** Do none of the above if the rest of the truck is not in top shape, like brakes tire etc. Going fast is really gonna suck when you cant stop or steer***
Ok Stock motor, this is the "realm" I am working with.
I have recently rebuilt the engine in my 92 SE-5 FI 2.2l. Bored .020, decked .004 and head shaved .010
Based on calcs I have used n the net and my own human error, I have come up with about a 9.17:1 compression ratio. I spent 18 hour blending the valve seats to the int/ext ports mirror finishing the ext ports and putting a satin finish on the int. ports (better in comming fuel mix. Even added a K&N conical filter like all the ricey newbs do hehehe.
these mods alone have made my lil 4banger feel like a small v6. The top end (above 75 mph) is still lacking though, but this may be a fuel problem, as I suspect a faulty fuel pump. Not to mention these trucks just weren't made to break wind hehehe. Allthough with the tail gate down I have gotten 117 mph top speed.
I know this is getting long winded hehehe, but one last thing to remember is that my engine is the multiport FI 2.2l. Perhaps the same or even more power could be gained using side draft webers on a carb motor, but this info I do not know.
Its like this, if you want to keep yer mazda... MAZDA RX7, MX6 Turbo, and a stock motor build-up are your options. Least the ones that I know of that work.
Building the stock motor for power is harder, but I must say I certainly know ALOT more about power building as a result.
I guess building your own engine mods when there is little to nothing available "bolt on" defines one as a TRUE hotrodder.
I float around this board from time to time, but if you have any questions give me a buzz at xenodraken@hotmail.com
Cya!