For the MKARS80, can it be modified to use the entire 80/75 meters band that
hams in the U.S. have which is 3.5 thru 4.0 MHz.
Hi Sam!SURE! 
It's a
very simple mod and it's included in the rig's manual.
If I recall correctly it's only a matter of changing the number of windings
in one of the ferrite inductors in the LO circuit. With the Polyvaricon
tuning scheme, I had about 350 KHz coverage. That is a LOT
of frequency to cover in a one turn Polyvaricon (which really
only turns clockwise from about 7 oclock to 5 oclock.)
The MKARS also has a "Fine Tuning Pot", which becomes fairly
useless if you install the Ten Turn Tuning Pot Mod, hihi.
When I changed that to the Varicap & Ten Turn Pot tuning
Mod (a super simple mod....three parts) the freq coverage
almost doubled. OR you build it with the stock Polyvaricon
and add a simple switch and a small cap in the LO circuit
to shift the frequency coverage up or down.
(
It sounds a lot more complicated than it is,haha.The instructions clearly outline how to do either mod.
After all, a lot of MKARS are sold in the USA)
If I were you I would buid it "stock" for the US frequencies and
the included Electret Mic,
then modify it for a Dynamic Mic instead.
You remove the bias resistor R17 in the mic circuit, or add a series
capacitor, because electret mics need a small current to work.
I use a cheapo used CB mic I found at a garage sale and it works super.
I can send you all the mods or links to these mods.
I am only a General right now, and I can only do CW and digital data modes
from 3.525 - 3.6 and then SSB and Image modes from 3.8 thru 4.0.
This kit was designed basically as an 80m version of the famous BITX20
minimalist SSB QRP transceiver. I do not know if it is frequency stable enough
for data modes, even with the Varicap Tuning Mod. I kinda doubt it.
BUT.....I see at the web site there is a VFO Stabilization Mod
that just switches out two regular caps in the VFO for Polystyrene caps.
They used to sell a CW Conversion Kit for the MKARS 80 but
it is discontinued. I bought one and still have it,
unbuilt. My MKARS
works so well I didn't want to fidle about with it anymore! The CW Conversion
Kit is yours for $25 plus postage, that's less than what I paid for it.
HOWEVER...I would build the rig first and see what your comfort level
is with mods. The MKARS CW Conversion Kit involves a lot of fiddling
about with your finished rig...which might be why they didn't sell many,
though I don't know that as fact.
Also, any idea how much that would be in U.S. dollars?
Answered above...
and that price *includes shipping* to the USA.Seems he does not have cases in stock for the radio kit.
THe MKARS Web Site says something like "cases expected after Dec 16".
Maybe Steve never updated that.
Drop him an email and ask him. The enclosure was cheap when I bought
it, about $7, You can't find
any all metal enclosure that cheap anywhere.
If you get desperate for one,I still have mine. I built my MKARS
into an enclosure with more room. (I added an inexpensive PIC/LCD
SWR/PWR Meter). You can have the case for $5 & postage if you want.
My email good at QRZ, or address good in any Callbook back to 1986.
In summation:This is a FUN to build and great performing minimalist 75m
QRP SSB rig that can be easily modded for USA freqs.
BUT if you are interested in an 80 CW QRP Kit rig,
I would make another choice.
GL ES 73, Ken Pendarvis, AD6KA / 5R8GQ