Morning all.... I've a few questions about the 4.2 XK 6 cyl engine

I have a 69 E-type, I'm going to rebuild the originial motor, in the interim, I'm looking for a later model XK engine to drop in so I can drive it....

I have an automatic... are the belhousings the same? will a later automatic work in my E?

1) what is the best year engine to use that is
a) plug and play
b) can be hotrod's later after I take it out....

Are some years better than others? bigger valves? better flowing heads?

If I wanted to use this motor full time, is there an advantage over a later one than my original 69 motor?