V6 swap

Hello,
In addition to some other info in this forum for swapping the V6 engine to a 350 I wondering the following; V6 in my 1992 Silverado is approaching the magic 300.000 miles and is still running fine. However, I want the V8 in it.

As this is the 4.3 TBI engine can I put a vortec 305 in it or is it better to have a 305 TBi installed. Can anybody tell me which parts need to be changed: electronics? Can I use the stock computer of the 4.3TBI for the 5.7 ??

Currently I have a 5 speed gearbox; do I need to change anything on it in order to fit the 350 engine?

Last question, is a stock cylinder head of a 5.7 ready to run on propane or should I change valves / valve seats?

Thanks in advance
Melvin
amsterdam
Holland