Lets say I bought a pair of 540 Dart shortblocks, Gen IV style. Would it be possible to install my rect 188 heads off my 454/420, new HYD flat tappet cam, intake, and larger oil pans? Would I still be able to use the 9022 Holley 800's or would I have to go to 850's or 1050 dominators? What else would be needed to be done, and would I be able to make 550-600HP with this combo?

I did with port/polish/gasket match/bowl blend on my 540cu in. Combo made 600hp with dyno headers. It will make more as I did have my static CR low in case I ever wanted to add a blower. I probably left 50-60 hp on the table. EMI 4" wet exhaust probably cost about 40-50hp, another 15hp or so for accessories.

Rule of thumb for carb sizing is: cu in X max rpm / 3456 = carb cfm (this IS AT 100% VE). Unless you have great heads on an N/A engine, this gets pretty tough to achieve. It will get you into the correct size carb, however.

With a hyd. flat tappet cam you will have a hard time making more than 550 hp. In this case the 800 would be enough carb. For a higher winding 540 with good heads, a 1050 will usually make more hp. A good hyd. roller would be good for 50 more hp. The heads will work ok though.

I agree with PatiYacht. Also, I think it was Las Mesa who said he made something like 660-670hp on his dyno with a hydraulic roller in a 555cid engine using a 800cfm Holley. Don't remember what heads he had on the engine though. Have fun.