You have a real problem... you have a 996R and its spoilt you!
but...
Any of the testastretta frames or 748R or 748RS have the lower cross bracing and repositioned coil mounts (and larger engine mounting bolts)
basically because these models have shower flow injectors and larger airbox's.
A 996SPS motor will go straight in, as will 996S, you could then use your 748 loom / ECU with a new Eprom, and use a set of 916 or 996 (with 1 injector unplugged) throttle bodies, you could use your 748 ones but it would be best to get the WSS 45mm restrictors removed.
However, you just can't beat a Testastretta!, if you can find an S cam'd motor (998S or 996R - good luck) complete with loom and exhuast headers from a breaker then you are laffing!

