Im having glassdave redo the transom/ stringers in the scarab and also raise the x dem. Im going to need to mock up the motor mounts so i was thinking it would be easier to use a mock up block for that task. Does anyone else do it that way or is there an easier/better way?

Why don't you just raise the motor mount blocks the same amount you are raising the x-dimension...I'm assuming your motors were lined up properly before the transom work when I say this.
Are yours standard screw adjustment type mounts ............or race mounts

That was my original though but he is cutting out the stringers too.

You might want to check out the plastic mock up engine blocks sold by Summit/Jegs. I would think it would make the job much easier.

There's got to be a junk BBC laying close to Dave that can be used for mocking up. Also don't forget about standard vs tall deck for exhaust locations....

Are you using flat pad mounts or a plate mount. Either way you will need a block, crankshaft with bearings, flywheel, coupler, bellhousing and alignment shaft. If Bravo, if trans. same process.
If using pads, add amount to stringer or some installations use a L bracket supported with gussets thru bolted and the mount bolts flat to bracket. Motor plate, well you will need L brackets 3x4-5x 3/8 with backing plates. Fabricate brackets, locate clamp to motor plate and drill stringers, bolt up, then you can locate and drill holes in L brackets.

You can't use the plastic mock up block in this situation since it doesn't have a provision for a flywheel and coupler, which you will need to align the engine. As Mark said, you need a block, crank, bearings, flywheel and coupler. You can use some old junk parts, but they must be assembled.
Eddie