Hi! & Buffer circuit questions

[Sickle]

Hi all, I am new here, but so far I have found this forum very enlightening & helpful (even the stuff I didn't understand )

Have been a member for a few months trawling through all the very helpful info, but I have not had to post as all questions had been posed already . So far, I have modded my valve junior, built a GGG Rodent from scratch (very happy, great circuit) & modded my DOD Grunge as per some recommendations here, having a ball

I have a few questions regarding a buffer/blender I am building to blend clean bass signal in with a Big Muff (or any other pedal): basically I want a buff & blend, like this http://seanm.ca/stomp/minblend.html. I have some velleman preamp kits (K1803) lying around which use the UA741 op amp, I figure I can make these work. The details are here:
http://www.vellemanusa.com/downloads/0/illustrated/illustrated_assembly_manual_k1803_rev1.pdf , (schematic is on the last page)
but I need some suggestions on changing the input & output impedances, to 1M & 100K respectively.

Based on the input of my modded valve junior, I thought a 22k res in series(R1)  & a 1M res to ground (R4) on the input would work (same signal right?) & a 100K res on the output would do the trick, can anyone tell me if this will work? I will be adding a 50K blend pot to the output, so should I use a 50K res instead? Or should I start from scratch?

(I realise I could measure the imp, swap res until it is right, etc, but I figure I wouldn't learn why, just the how!)

Thanks in advance!

(BTW, it is really good to see some big names in the pedal world posting regularly in here.)