Maybe I'm living in the past, but you should be able to freshen up that motor for a LOT less than 10K. I would think $5-6K IF you do all the work.
That said, leave the 912 as a 912. If you want to keep the car keep it a 4 cylinder. There are options out there that won't require a new mortgage. Like a T1. They are easily capable of around 200hp.
That 2,2 E motor is one of the best motors Porsche ever made. At our (PCA Redwood) last AX there were two 2,2 Es. Honestly they screamed. Embarrassed a lot of new watercooled stuff.
Honestly a 2.2 E in a SWB car would be awesome, but I would bet you would ultimately regret putting a 6 in that 912, IMO.
Also, by putting a big bore set of cylinders on that 2,2 you can easily see 200hp.
I would look for a roller for that 2,2.
Here is a 912 with a warmed up 1750 that turned more than one TTOD. Unfortunately lost to the fires.
