creds: I did a 912 conversion on the ghia pictured in my Avatar (since backed out and returned to stock).
Yes - Shad Laws is the guy to talk to about Type 4 conversions for Ghias. If I had to do it all over again, that's probably the route I would have gone, because though the conversion is more difficult, Type 4 engines are a bit cheaper to rebuild.
I second the opinion that putting a 901 transaxle into a Ghia is a non-trivial project. Consider a Gene Berg 5-speed kit. You spend more up front, but there's less hacking done on the Ghia body. Overall, the cost is about the same. The 901, of course, will be more durable (depending on the condition in which you obtain one).
If you want to do a 356/912 conversion though, I can offer a few words.
Yes - it's a lot of fun driving a Ghia with some cujones. The Type 4 engine is probably more durable (depending on how it's built, of course). It's got a full-flow oil filter, which the 356/912 does not have (though it can be modified for one). Type 4 is a tad heavier, which can be a concern for a tail-dragger. And the conventional wisdom says you've got to convert a Type 4 for upright cooling. Not so for a 356/912. Also, valve adjustments for the 356/912 are a bitch, for the Type 4, nearly impossible (some people may disagree with that assertion).
If you're considering a 912/356 conversion, Richard Troy at www.karmannghia.org can steer you in the right direction. He's got a 912 engine in his double-cab.
For my 912 conversion, there are the following concerns:
Throttle linkage: you've got to convert earlier in the chain from the cable-system of the VW to the Porsche ball/rod/bellcrank system on the back of the fanshroud. I had to fabricate parts (had them fabricated).
Carb clearance: ANY dual-carb setup in a Ghia has this as a concern; air cleaners can interfere with the decklid springs. Two solutions: low-profile air cleaners or remove the decklid springs and prop the decklid with a stick (bleh!).
Exhaust/Heat: 100% custom, as far as I know, is the only solution. I bolted a stock Empi crap muffler onto the flange of the custom headers I bought. That lasted about 3 months and rusted out! (muffler was about $50, so.. . ) then I tried to modify a Bursch 912 header/muffler system, which only kind-of worked, and I ended up sawing off the muffler, welding on a flange, and bolting it to my header. Never did work out the heat problem. Oh yeah I did - I wore a jacket!
Clutch: This issue changes depending on the YEAR of your Ghia. I had a late transaxle, but the clutch arrangement changes between 67-ish and 72-ish. You DEFINATELY want a "freeway flyer" Type 1 transaxle, at the very least. If you're getting a new one anyway. It's got a good ratio for a higher top-speed. With the stock T1 engine and that transaxle, there's an annoying "gap" between second and third, where at around 35 mph, you're either lugging or revving high. 35 is a very common speed to drive at, no? You won't notice this gap with the Porsche engine. Trust me. With the freeway-flyer tranny, you can top out at 85 with the stock engine. With the 912 engine, on a hot day at Furnace Creek, CA, I did 110. With the top down. Loaded with camping gear. It still had some legs, but I wouldn't push it any faster without ground-effects. The Ghia's not a good shape to be pushing any faster than that, without going airborne.
So for the late transaxle, using the Porsche clutch (215mm?) I had to clearance the bell-housing for the flywheel, and I had to use a 6mm shim on the starter to mate the starter teeth to the flywheel, and I had to use a porsche Throwout Bearing, a custom guide-tube, and a custom throwout arm to hold the bearing. I guess you can also get a VW flywheel modified to fit the 912 engine, and use a VW clutch, which means you don't have to mess with all the custom clutch bits.
Oh, also, I had to use an autostick starter instead of the regular starter, because the regular starter has a bushing that will interfere with the larger flywheel. The autostick starter is a bit stronger and beefier.
I drove this combo for about a year - but I realized I had bad rings, and would have to rebuild the 912 engine. When I found out how much that was going to cost, I put the stock engine back in. The 912 engine's still sitting in my garage. I can't bear to sell it, can't afford to fix it.
There are also folks who advocate hotrodding the Type 1 engine. You can go a long way with this - conventional wisdom says that a hot-rodded VW T1 engine won't last as long as a stock 912/356 engine. The VW advocates will disagree. I'm not sure what camp I fit into - I didn't have a fresh 912 engine to work with.
I hope all this rambling helps.