Lq9+t56=mpg??

I'm researching the idea of swapping an LQ9 (Silverado SS HO 6.0) into my '88 Trans Am. I've already got an LT1/T56 in there now. I work at a dealership and work on these trucks everyday, so I'm thinking the newer engine would be better.
I was wondering, if I got the engine from GMpartsdirect and got a used wiring harness, and LS1/T56 bellhousing to put on my current T56, anything else I might need?
Anyone know what kind of MPG I might get with 9" with 4.11's?

Don't forget the rest of the LS1 transmission, since you would need ALOT more than just the bellhousing to make your current T56 work. I would expect the mileage to be very close to what an LS1 f-body gets with 4.10's.

How so? I was sure that just an LS1 bellhousing mated to a T56 would bolt up and work fine...? What else would I need?

Depends how your current clutch is setup. The LS1 bellhousing has no provision for mounting a slave cylinder, if you currently have an "LT1" T56. Or, if you were running a mechanical clutch linkage, the problem is obvious. The "LS1" T56 has provision on the front plate of the tranny to mount the slave cylinder concentric with the input shaft. The LS1 bellhousing is set up to support only that configuration. The LT1 front plate does not have the provision for mounting the concentric slave.

I also underestand the "LS1" style T56 has a longer input shaft than the LT1 style, so there might be other dimensional issues.

McLeod makes an SFI-rated "universal" bellhousing, but I believe they only make it to work with the LS1-style T56, because they want to avoid the issues of the LT1-style with the pull-back clutch design.

Just sell the LT1 T56 and buy an LS1 style. You wont lose much money because they are worth about the same. It will also save you cash from buying a custom bellhousing.