Your pretty limited on what will fit into the 320, was the L16 a conversion that was done right, or was it just shoe horned in there and called good?
Does it have a heater anymore, almost every L block conversion I have seen in a 320 deleted the heater box, as the engine was so close to the firewall there was no room for the heater hoses anymore.
I like the A15/dual SUs with a 5 speed in the 320, it moves along alright, and the only sheet metal that needs cut is the shifter hole for the transmission, of course it helps to have the 1965 320 tunnel cover also.
Not a lot of guys doing 320 conversions, I know of one Mazda rotary 320, and one Nissan VG30 320, I have never rode in either to say if it was a good thing or not.
VG30 320 build
http://community.ratsun.net/topic/46269-30l-v6-l320/
Rotary 320 build
http://community.ratsun.net/topic/36253 ... 320/page-7
As i mentioned, I like the A15, 5 speed with dual SUs, it was my very first real conversion, but I did it before joining any forums, so there is no build thread, just a couple photos.

A kid hit me head on, I sold it soon after.

Take some more photos of the truck, and some of the engine compartment.