Stack 64cm, reach 46cm. So.. 18,5" is definitely to small

Hello everybody. My second post here. I tried searching, but came up short. This is my dilemma. I'm 186-187cm (that's 6'13"). My inseam is 89cm (35"). I have some serious back problems (herniated disc), and a bit longer arms that I should. I weigh up to 225pounds with my gear. So.. not a small guy.

I have a local forum member selling a workswell 062 frame in size 18,5". The customer service says I can use 20", but I can fit 18,5". Not much help there.

My current ride has a TT of 610cm, and ST of 49cm. The 062 has TT of 620cm, and a bit lower ST (47cm) which is not a problem, since i have almost 15 cm of seatpost to spare.

I find my current bike fit pretty good. My stem is 90mm long, and the seatpost has a slight setback. So in theory, with a 1cm longer TT, and with either the same post or a straight one.. the 062 could fit me great. All other dimensions like HA and WB are almost spot on.

Any real life experiences of tall-ish riders out there?

I strictly ride and XCM rides, forest trails, gravel, dirt... ad a little of root and rock. Nothing overly technical.

will the frame assplode under me? (the workswell said the frame is good up to 200kg).

help me out before I spend all my kids lunch money....

I'll attach the pic of my current ride...