It can be done. Get a type 4 engine with flywheel and clutch attached and it will fit right in.

How do I know, cause my car had a type 4 motor in it when I bought it.

You can make up the mounts no problem if you need some photos I still have the mounts in the shed.

I toyed with the idea of putting hot type 4 in the car, but decide to go with the Porsche 6

912e motor
 

Do you have a 912e motor?

no, a 912E trans is needed because the 915 mainshaft is larger diameter than the 912E and won't fit the 4cyl disc, and the 915 has a pull clutch setup and a 912E is a push type as well as a difference in guide tube diameter. and you can't convert that stuff as the bellhousing design does not allow it. that said, i need a 912E ring and pinion setup with shims.

thought about the flat 6 out of a subaru?

What ever happened to Steve Stromberg?

I second the "third" the beater proposition! Way way back when I was 23, in a far-away place, my 911 engine needed a rebuild. I drove my parent's extra car, a '67 Chevelle 4-door station wagon for 3-months. That was a shameful experience at the time and provided ample motivation! But seriously, pick a good-enough beater that you can 'flip' at the end of the project! (Come to think of it, we should have kept that station wagon... considering what people would pay nowadays!)