[Henry Schmidt]

A great engine to build using the 2.7 as a base platform is a variation of the 2.7 RS spec engine.
You already have most of what you need.
Do the machine work required for a stable bottom end (plenty of information on the forum), install CaseSavers and good studs, replate the 90mm cylinders, buy 9.5:1 JE pistons. Port the heads to 36mm, select the cams that suit your sensibilities (I like Mod"S" but Solex, Mod Solex and "E" cams will also make a reasonably fun engine) and rejet the Zeniths. This can be a challenge but making the Zeniths work has been done.
The reason for building a 2.45 is to use the 4R case without boring the spigots which creates a poor platform for reliability.
If you have a 7R case, build a 90mm motor.