Johnnie
there is a whole heap of engineering involved in any conversion - chevy small block is the easiest, but you said you just want a reliable engine with decent power.
I have a solution
There is a 4.6 range rover on ebay for 1500 quid - has top hat liners etc all proper.
I have spoken to the owner James - nice chap.
He lives in winchester and the car is at his oldies' place in yourkshire where it has been sorned for 18 months as he does not use it.
He has all the bills for the rebuild and the liners were fitted by oldsworthy engineering in winchester.
I was thinking of buying it as a tow tug but a disco V8 with top hat block came up so I bought that instead.
Apparently it runs perfectly
Buy it - take the engine out and strip it down to to the block, put a kent H180 in it, new lifters and timing gear, reassemble with composite head gaskets and new head bolts and you will have a great engine, about 240 bhp and over 300lbs of torque
you will also have a spare gearbox, etc etc etc etc
here is the link
RANGE ROVER P38 4.6 ENGINE V8 GEMS TYPE 1994 - 1998,With Top Hat Liners. | eBay