i also have a '81 mark2b
i bought it without reverb, because back then, i was more into digital delay.
over time, i added digital reverb thru the fx loop, and unless i was driving the output section into serious saturation, the fx loop reverb sounded just great.
for recording, i run pure amp, and add all time effects post-mix.
so, the question is:
how hard do you plan on running the amp?
to use the FX loop, you can overdrive it if the levels are too hot....
but i've always had efx that had output and input level control, so it's never been hard to dial the levels in just perfect.
with using the loop only, you have the opportunity to use multiple efx units, with several different reverbs, including spring reverb, so you're not locked into just one reverb tone.